# String Manipulation and Matching Algorithms

String manipulation and matching algorithms play a crucial role in many applications, including competitive programming. These algorithms enable us to efficiently perform various operations on strings such as comparing, searching, and manipulating them. In this article, we will explore some commonly used string manipulation and matching algorithms in the context of competitive programming using Java.

## String Comparison

When comparing two strings, we often need to determine whether they are equal or not. Java provides the `equals()` method, which compares the contents of two strings for equality. This method returns `true` if the strings are equal and `false` otherwise. For example:

``````String str1 = "Hello";
String str2 = "World";

if (str1.equals(str2)) {
System.out.println("The strings are equal");
} else {
System.out.println("The strings are not equal");
}``````

In addition to `equals()`, the `compareTo()` method can be used to compare strings lexicographically. This method returns a negative, zero, or positive value if the first string is less than, equal to, or greater than the second string, respectively.

## String Searching

String searching algorithms help us find a particular pattern within a larger string. One of the most commonly used string searching algorithms is the Knuth-Morris-Pratt (KMP) algorithm, which efficiently finds the occurrence of a pattern within a given string. In Java, we can utilize the `indexOf()` method to implement the KMP algorithm. For example:

``````String text = "Hello, world!";
String pattern = "world";

int index = text.indexOf(pattern);

if (index != -1) {
System.out.println("Pattern found at index " + index);
} else {
}``````

The `indexOf()` method returns the index of the first occurrence of the pattern in the text, or -1 if the pattern is not found.

## String Manipulation

String manipulation algorithms allow us to modify or manipulate strings in different ways. Java provides various methods for string manipulation, such as `substring()`, `replace()`, `trim()`, `toUpperCase()`, `toLowerCase()`, and more.

The `substring()` method allows us to extract a portion of a string by specifying the starting and ending indices. For example:

``````String str = "Hello, world!";
String substr = str.substring(7, 12);

System.out.println("Substring: " + substr); // Output: "world"``````

The `replace()` method replaces all occurrences of a specified character or substring with another character or string. For example:

``````String str = "Hello, world!";
String replaced = str.replace("world", "Java");

System.out.println("Replaced string: " + replaced); // Output: "Hello, Java!"``````

These string manipulation methods can be combined and utilized creatively to solve various string-related problems in competitive programming.

## Conclusion

String manipulation and matching algorithms are fundamental tools in competitive programming. Understanding these algorithms and being familiar with their implementation in Java can greatly enhance one's ability to solve string-related problems efficiently. By leveraging the provided string comparison, searching, and manipulation methods, participants can tackle complex problems that require handling strings with ease.

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