Java string contains time complexity. Definition and Usage The contains() method checks whether a string contains a sequence of characters. Among these operations, checking for the presence of elements can be particularly useful. Therefore the complexity is O (1). May 21, 2023 · In other words, how can Map. replace () section, It’s time complexity depends on nature of pattern Time Complexity: Oh (its complicated) Space Complexity: O (n) — Because y’kno Apr 24, 2011 · As the title says, I was wondering what the time complexity of the contains() method of an ArrayList is. The IndexOf method returns the index in the array where the sequence of elements first match. Additionally, as of Java 7 Update 25, even String#substring() is linear time because structural sharing actually caused more trouble than it avoided: substring of a huge string retained a reference to the huge char array. This is because you create n strings, and string creation in java has memory usage proportional to the number of Jan 16, 2017 · What is the time complexity of the String#substring() method in Java? Jan 4, 2025 · Note: The same operation can be performed with any type of Mappings with variation and combination of different data types. This is because the . Any toString method where the returned string contains the object's contents in some form obviously can't be O (1) (you can't create a string containing n items in less than O(n) time). If you had objects in the For example, substring's Big O complexity is O (n), while charAt is O (1). Along the way, it explains various HashSet Mar 14, 2013 · In Java, the complexity of s1. Turning that into the complexity of a sequence of concatenations is difficult in general. Apr 15, 2017 · A program I'm working on converts an array of integers to a string using string builder. append("GFG"); Time Complexity for concatenation This lesson delves into the concepts of complexity analysis and optimization in Java using the Java Collections Framework. Aug 25, 2013 · I know the brute force approach with the time complexity of n*m (m is length of first string and n is the length of the other one) for testing if an string contains another one, however, I'm wonder I did a small trivial test of the "contains" method using random strings on Java 17 using TreeSet, HashSet and ArrayList. equals() method and what the runtime complexity of such an operation is. Like you said, there could be multiple collisions that result in a longer processing time than a O (1) algorithm would imply. Keep coding, keep learning, and happy string manipulating! Oct 12, 2024 · Learn how to analyze time and space complexity in Java with practical examples. 1. 8, as others mentioned it is O(1) in ideal cases. Did you test with much larger lists? Maybe the time difference is a constant time difference, independent of the list's size? Causes The `HashSet` class uses a hash table for storage, allowing for constant time complexity for add, remove, and contains operations, thanks to its hash-based structure. length * N) since append () copies the input string to the end of the StringBuilder N times? Yes. HashSet vs. Integers are immutable, so the space complexity would be 2n, which I believe simplifies to just n, since constants don't matter. Jul 19, 2023 · For example, String. The `ArrayList`, on the other hand, is backed by a dynamic array which requires linear time complexity for the contains () method since it needs to iterate through the Aug 13, 2025 · The time complexity of the containsKey () method in a HashMap is generally O (1), meaning it has constant time complexity. We saw the actual runtime performance of each type of collection through the JVM benchmark tests. Is each individual character checked (leading to O(N) where N is the length) or Feb 4, 2014 · The method contains of the HashSet class in Java operates in constant time. String. 6 or more elements, HashMap is faster. containsKey () considering that you are using a HashMap since searching in HashMap is done in O (1). contains ()` method is used to check if a certain sequence of characters is present within a string. Feb 26, 2014 · I'm wondering how Java implements the String. The break even point is around 5 elements in the collections. split(""); or String[] stringArray = s. contains (String) is implemented using String. Jul 21, 2011 · i believe its O (n) because you loop over the array, and contains and add should be constant time because its a hash based set. UsIng different methods to solve this problem and check its time and space complexities. Contains() is only useful for checking the existence of an exact sub­string, whereas Regex allows you to do more wonders. In summary, the time of execution grows quadratically. My above solution's time complexity depends on the complexity of HashMap. Jun 27, 2019 · Should this have time complexity of O (inputString. Example: Here, we will use the contains () method to check if the ArrayList of Strings contains a specific element. Example: Jul 17, 2021 · 3 In a nutshell, I am confused whether the time complexity of checking whether a String exists in a HashSet is O (1) or O (m), m being the length of the longest string being checked. split(" "); I'm wondering what would be the complexity(in O(string len Aug 28, 2025 · Is the Time Complexity of an Algorithm/Code the same as the Running/Execution Time of Code? The Time Complexity of an algorithm/code is not equal to the actual time required to execute a particular code, but the number of times a statement executes. What is the time complexity of string contains? contains () definitely uses naive approach and equivalent to O (nm) time complexity. Hence the O (1 Mar 6, 2022 · Is it O (n) or O (1) (by saving the length in a private variable during string allocation to the object)? if it is O (n), does it mean that the complexity of following code is O (n^2)? for (int i=0; i&l String manipulation operations are some of the most common tasks in programming, and analyzing the time complexity of string algorithms helps us understand the performance characteristics of these operations. I was wondering whether startsWith is faster than indexOf. charAt (i)) is a linear operation because Java strings are immutable. For example: Write code in C/C++ or any other language to find the maximum between N numbers, where N Dec 10, 2024 · In Java, the ArrayList contains () method is used to check if the specified element exists in an ArrayList or not. Continue reading for more detailed information and advanced usage scenarios. So, as far as I can see, the performance difference should be minimal. I’ll post updates every w It says Mobile (android), anyone know the best way to preapre for this and what to expect? Jan 29, 2015 · 10 I had tried both approaches and repeated them over 100k times and String. The includes method has an O (n) time complexity, where n is the number of entries in the list, and it does not require Aug 26, 2014 · You cannot possibly create a String from a StringBuilder in constant time and have its immutability maintained. O (1) implies that the processing time doesn't necessarily correlate to the number of elements in the container, which is true for hash sets. ArrayList has the following info: "The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. This efficiency is due to the underlying hash table structure of HashMap. Program to Check Two Strings Are Anagram Of Each Other in Java Below is the Program to check if two strings are anagrams Java using Sorting: We would like to show you a description here but the site won’t allow us. I'm trying to determine the time complexity of this approach. Jul 15, 2014 · This important thing is that the contains method is called on the other Collection and so the complexity is dependant upon the complexity of the other Collection contains. Use a StringBuilder — now addition of a character can be done in constant time. ArrayList: Internal Structure HashSet is backed by a hash table, allowing for constant time complexity, O (1), for basic operations like contains, while ArrayList is backed by an array which entails a linear search of O (n) for the contains method. I want to know what is the time complexity of below two statements in Java: // statement #1 Jul 31, 2024 · Thank you for joining this journey into the world of string algorithms in Java. It stores key-value pairs in a sorted order using either a natural or custom comparator. containsKey () is O (1) in Average Case, and O (n) in worst case. Until a match is found or the end of the list is reached, it repeatedly goes through each element in the list and compares it to the target element. We can prove this by using the time command. Dec 8, 2013 · This performance difference surprises me. containsKey () search without iterating over the elements in proper sequence like List. equals method checks each character of both strings for equality sequentially until a difference is found or the characters are exhausted. replace has to at least be O (n) because it has The time complexity of lookups in a HashSet is generally O (1), meaning it takes constant time to check if an element exists. Internally uses Hashing, hence allows efficient key-based retrieval, insertion, and removal with an average of O (1) time. The method returns ‘true’, which we print out. Jul 11, 2025 · TheString. Space complexity is actually O (n*m), where n is the number of nodes and m is the length of the largest string you will create (which is the last string which contains all the words). 3. contains () method The contains() method checks if a specific element is Java "requires" that two objects which are equal (by equal ()) have the same hashCode. Boyer-moore takes O (nm) time in the worst case. This turns the searched-for String in to a Regex, containing a Program, which contains a DSLTree, etc. Provides O (log n) time for insertion, deletion, and lookup. Time complexity of the ArrayList contains () method After seeing the internal implementation of the contains () method, we know that the time complexity of the contains () methods is dependent on the indexOf () method. contains () does, which is what makes List. Hey everyone 👋I’ve just created this new LeetCode account and decided to stay consistent this time. But in that scenario, the time complexity of a string key and an integer key are both non-constant. indexOf (“. So it depends. I would also add that other basic operations, such as add, remove, and size also operate in constant time. Time Complexity: Time Complexity of HashMap. Understanding its time complexity is essential for optimizing performance in applications, especially when dealing with large strings or frequent checks. List. My goal: solve 100 LeetCode problems in the next 60 days using Java, focusing on Arrays, Strings, and HashMap patterns first. Below is a detailed breakdown of the major operations and their time complexities. println(b); I run the Java code above, the b return true. For example, "abcd" and "dabc" are an anagram of each other. Jun 24, 2024 · The Java 8 Stream API provides various methods for operating on sequences of elements, such as filtering, mapping, and collecting. HashMap is not thread-safe, to make it synchronized, use Collections. In Java, the `HashSet` data structure is widely regarded as the fastest option for performing `contains ()` operations, offering average time complexity of O (1). Sep 5, 2018 · This article presents the time complexity of the most common implementations of the Java data structures. containsValue () method. Using List. The contains () method calculates the hash (O (1)), indexes into the hashtable (O (1)) and verifies their equality (O (1)). contains () Method: List contains () method in Java is used for checking if the specified element exists in the given list or not. prototype. The add operation runs in amortized constant time, that is, adding n elements Jul 4, 2011 · A look-up operation OR contains for single can be O(n) in worst-case right ? So, for n elements look up in hashSet will be O(n^2)? Oct 8, 2019 · Time Complexity of Java Collections 1. concat(s2) or s1 + s2 is O(M1 + M2) where M1 and M2 are the respective String lengths. In this article, we will learn how to effectively use the string contains functionality in Java. length)? It is O (1) when appending single characters. Syntax: public boolean contains (Object) Paramter: It takes a single parameter Object which to be searched in the given list. firstMatch (of: some RegexComponent). May 20, 2022 · 0 I have to split a string using comma delimiters and lookup a value in it. In Java 6 and earlier, the method operates in O (1) time, while in Java 7 and later, it operates in O (n), where n is the length of the substring. Otherwise, it will return false. and Values can be duplicated. contains() is a lot faster than Regex. Oct 15, 2025 · A TreeMap in Java is a part of the java. Oct 11, 2020 · Can anyone help me to figure out that, is there any collection type in java (or any language agonistic one) that offers O (1) time complexity for indexOf(Item item) operation? Jan 19, 2024 · For Java developers, Big O notation isn't just a theoretical concept—it's a practical tool for evaluating the efficiency of code. Sep 22, 2024 · Unlock the secrets of Java Streams! Discover common pitfalls with `contains` and learn best practices to elevate your code from good to exceptional! The time complexity of the HashMap. Java: set of Contains () method time complexity, Programmer Sought, the best programmer technical posts sharing site. Oct 14, 2024 · Understanding Why HashSet Provides O (1) Search Time Complexity In the world of Java programming, efficiency is key. Please shed some light on the time complexity of containsValue () method and suggest me if there is any better solution for the above problem in terms of time complexity. Let us delve into understanding the contains, containsAny, and containsAll methods in detail. Aug 29, 2016 · String is immutable and in each sentence variable assignment new String object is created . One of the most efficient data structures for storing unique elements is the … Jul 7, 2025 · Learn how Java contains () method checks if a string contains a specific sequence of characters. Example : StringBuilder str = new StringBuilder(); str. 4 or less elements, ArrayList is faster. Includes syntax, usage, and return values. This efficiency stems from the underlying implementation of HashSet, which uses a hash table to store its elements. Jan 19, 2012 · The time complexity of containsKey has changed in JDK-1. Oct 27, 2025 · A HashMap is a part of Java’s Collection Framework and implements the Map interface. A toString method that just returns a fixed string (like Object. The implementation of indexOf() in early Java versions used a naive string matching algorithm with O (n*m) time complexity. ”) with the String. A StringBuilder is like an Nov 19, 2024 · In Java, the String indexOf () method returns the position of the first occurrence of the specified character or string in a specified string. Perfect for Java interviews and optimizing code performance. It stores elements in key-value pairs, where, Keys are unique. Did the people that write those answers on SO inspect the source code of the String API to figure the complexity out? My string is of type"abacsdsdvvsg" or"a a a a a a a" And I use String[] stringArray = s. See full list on baeldung. However, this can vary due to factors such as hash collisions and load factors. The behavior of substring() has significantly changed over various iterations of Java, affecting both performance and memory consumption. Jul 12, 2023 · The contains () method The contains () method is a quick approach to determine whether a list contains a particular member. Dec 17, 2022 · 2 This question has not been asked before, since I am specifically asking O (1) constant time after the time taken to preprocess the string is amortized over many freq operations. In the string world, the size of string is k where k is the length of string. An interviewer asked me to find the total count of a character appearing in a substring. A common area of confusion stems from the time complexity of this widely used method. It starts by demonstrating a brute-force approach to finding common elements between two lists, examining its inefficiencies. Due to hash collisions, the indexing step may have to probe a few subsequent elements sharing the same hash, which in worst case can be O (n), but Time complexity is O (n), where n is the number of nodes, because you iterate over each node once. find_first_not_of () finds and returns the position of the first character that does not match a specified character (or any of the specified characters in case of a string). util. Mar 6, 2022 · Is it O (n) or O (1) (by saving the length in a private variable during string allocation to the object)? if it is O (n), does it mean that the complexity of following code is O (n^2)? for (int i=0; i&l String manipulation operations are some of the most common tasks in programming, and analyzing the time complexity of string algorithms helps us understand the performance characteristics of these operations. This is a basic way to use the ‘contains’ method in Java String class, but there’s much more to learn about it. Feb 2, 2017 · 10 I am writing code in Java where I branch off based on whether a string starts with certain characters while looping through a dataset and my dataset is expected to be large. Java's ArrayList is a resizable array implementation of the List interface. When we talk about collections, we usually think about the List, Map, and Set data structures and their common implementations. A string is an object but is also a collection of char structs. The engine which executes this regex also has a bunch of heap allocations to represent its matching state, etc -- it doesn't know the regex you gave it is a simple string; it could be any Mar 23, 2023 · Quick Way (Not time complexity wise, but in terms of number of lines of code) The idea is to use find_first_not_of () in C++ STL. contains () generally should resort to sequential search or a binary search thus the complexity will be atleast O (log n) In which Big O notation time complexity does string comparison lie? Particularly when the strings are unbound and random. So you are copying the entire test string to a new buffer, adding the new character, and forming the new string. May 8, 2021 · Time complexity of checking whether a string exists in a HashSet Ask Question Asked 4 years, 5 months ago Modified 4 years, 5 months ago The time complexity of the `String#substring ()` method in Java depends on the version of Java being used. concat () One more way to concatenate Strings is by using the concat () method: Jul 11, 2025 · TheString. In Java, the `String. Understanding the time complexity of its core operations is crucial for performance optimization in Java applications. contains () have a linear time complexity? Aug 9, 2011 · So if you look at in in terms of how many strings are concatenated (and not the characters copied), you're copying the contents of the n strings by the time you reach the n th iteration and all that matters is the worst case (the last iteration). synchronizedMap We would like to show you a description here but the site won’t allow us. Therefore, the complexity of dynamic concatenation in a loop of n iterations is O (n^2). Jun 4, 2024 · Understanding the intricacies of Java’s substring() method is essential for any developer aiming to write efficient and performant code. containsKey () method in Java is O (1) on average. The contains (Object o) method in an ArrayList checks if a specific element exists within the list. Jul 23, 2012 · 0 Map. Parameters: s - the sequence to search for Returns: true if this string contains s, false otherwise Hello everyone! Does Oracle have any websites where I could find out what the time complexity of a method is? I know sometimes they have that information in the API; for example, java. Since the String Class in Java creates an immutable sequence of characters, the StringBuilder class provides an alternative to String Class, as it creates a mutable sequence of characters. Jul 23, 2025 · An anagram of a string is another string that contains the same characters, only the order of characters can be different. Since s2 is empty, why does s1 contains s2? I check the Java API, it write: Returns true if and only if this string contains the specified sequence of char values. Mar 7, 2025 · Consequently, increasing the number of iterations in 10 times, the running time grows to 4370. Sep 3, 2020 · It looks like usage of the String. May 21, 2025 · The indexOf() method has been part of Java since its initial release in 1995, making it one of the oldest and most stable APIs in the language. Jun 13, 2023 · The time complexity for basic operations (add, remove, contains and size) is constant time O (1), assuming the hash function disperses elements properly among the buckets. This blog post aims to demystify Big O complexities through real Java code examples, helping you visualize how these complexities translate in practical scenarios. 441 milliseconds. replaceAll method, in fact, makes sense, even for the empty input string, compiling and matching the pattern takes too much time Nov 22, 2024 · The time complexity of HashSet basic operations – add, remove, contains, and size – is O (1), with a good hashing function when used with user-defined objects. I did experiment with 2000 records but not found any difference. In Java, ArrayList#contains() calls ArrayList#indexOf(), which simply iterates over the array backing the list. contains () method is used to search for a sequence of characters within a string. Understanding its time complexity is essential for optimizing performance when working with collections in Java. 2. However, in case of collisions where the keys are Comparable, bins storing collide elements aren't linear anymore after they exceed some threshold called TREEIFY_THRESHOLD, which is equal to 8, Jul 23, 2025 · Method 3: By using StringBuilder (Best Way) StringBuilder represents a mutable sequence of characters. This article aims to clarify how In Java, the time complexity of the . Overview In this tutorial, we’ll talk about the performance of different collections from the Java Collection API. I understand that the bucket in which the string is going to be placed is determined by the hashCode() method of the string modulo the size of the HashSet. However, as Java evolved, the implementation was optimized. equals method when comparing two strings is O (n), where n is the length of the shorter string being compared. Sep 4, 2022 · Time Complexity: O (n) Space Complexity: O (n) If Separator string is more than one character, it is compiled into a Regex Pattern by Java for finding index to split, and as discussed in . I checked the docs and they don't mention complexity. Returns true if the characters exist and false if not. Feb 3, 2015 · System. Example: Jul 10, 2025 · Conclusion Time complexity is a fundamental concept in Java programming that helps in understanding the performance of algorithms. And then is should copy the previous value of the string char by char and the value of w . By manually analyzing code, using profiling tools, and following common and best practices, developers can write Java code with optimal time complexity. replace () section, It’s time complexity depends on nature of pattern Time Complexity: Oh (its complicated) Space Complexity: O (n) — Because y’kno Sep 4, 2022 · Time Complexity: O (n) Space Complexity: O (n) If Separator string is more than one character, it is compiled into a Regex Pattern by Java for finding index to split, and as discussed in . However String. . KMP takes O (n) time in the worst case. Oct 21, 2023 · In this example, we have a string ‘Hello, world!’ and we’re using the ‘contains’ method to check if it contains the sequence ‘world’. In this article, we will learn various ways to use indexOf () in Java. First of all, we’ll look at Big-O complexity insights… Continue Reading java-collections-complexity Careful! String concatenation (for example, test += str. out. Microsoft did something really smart here to reuse code, if a string contains an element/sequence it should also have an index, so they call the IndexOf method. What is the complexity of checking whether one string is equal to another? Jan 20, 2019 · Learn how to search a substring in a given string in javascript. The lesson then introduces the optimized solution using HashSet to drastically reduce time complexity. Jul 11, 2025 · Complexity Analysis: Time Complexity: O (nlog (n)) Auxiliary Space: O (1) 3. com Jul 27, 2023 · The built-in optimization and linear time complexity of the `contains ()` method make it an ideal choice for most substring search scenarios. I am thinking which way is faster splitting string in array and checking if array contains it or splitting string in Set and doing lookup in Set. If it were not hash based and required iteration over the entire set to do lookups, the upper bound would be n^2. toString, which just returns " [object Object]") would be O (1) though. Why do we consider that append () takes O (1) time complexity whereas it should be considered as O (inputString. Dec 16, 2014 · In terms of the complexity once you have a pattern pre compiled, you should approach the following complexity: On matches, it will take at least O (m) time, where m is the length of the string On mismatches (not a number), you can achieve anywhere between O (1) and O (m-1) time depending on where the pattern falls off the DFA. util package that implements the Map interface. However, in this same theoretical set, there could also exist keys that only take a single comparison to find. TreeMap internally uses a Red-Black Tree for efficient sorting. ai2n lmp hql jehk xg nsurl u4nun 006edk myi2pez7bw gh80vj5