Find First Occurrence

Published at10 Jan 2026

String Pattern Matching Easy 20 views

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In Find First Occurrence, you are given two strings: haystack and needle.

Your goal is to return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

For example, if haystack = "sadbutsad" and needle = "sad", the answer is 0 because "sad" starts at index 0. If haystack = "leetcode" and needle = "leeto", the answer is -1 because "leeto" never appears.

This is a fundamental string matching problem often known as strStr() in C or indexOf() in Java.

Example Input & Output

Example 1

Input

haystack = "sadbutsad", needle = "sad"

Output

Explanation

"sad" occurs at index 0 and 6. The first occurrence is at index 0.

Example 2

Input

haystack = "leetcode", needle = "leeto"

Output

-1

Explanation

"leeto" did not occur in "leetcode", so we return -1.

Algorithm Flow

Recommendation Algorithm Flow for Find First Occurrence

Best Answers
These are the verified best solutions for this Challenge. You can use them as a reference to improve your solution.

java

class Solution {
    public String reverse_string(String s) {
        return new StringBuilder(s).reverse().toString();
    }
}

javascript

function strStr(haystack, needle) {
    if (needle === "") return 0;
    return haystack.indexOf(needle);
}

php

function reverse_string($s) {
    return strrev($s);
}

python

def str_str(haystack: str, needle: str) -u003e int:
    if not needle:
        return 0
    return haystack.find(needle)

rust

fn reverse_string(s: String) -> String {
    s.chars().rev().collect()
}

typescript

function reverse_string(s: string): string {
    return s.split('').reverse().join('');
}

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Find First Occurrence

Example Input & Output

Algorithm Flow

Best AnswersThese are the verified best solutions for this Challenge. You can use them as a reference to improve your solution.

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Best Answers
These are the verified best solutions for this Challenge. You can use them as a reference to improve your solution.