Here, We see Find the Index of the First Occurrence in a String problem Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc., with different approaches.

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Find the Index of the First Occurrence in a String LeetCode Solution

Problem Statement

Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Example 1:
Input: haystack = "sadbutsad", needle = "sad"
Output: 0
Explanation: "sad" occurs at index 0 and 6.
The first occurrence is at index 0, so we return 0.

Example 2:
Input: haystack = "leetcode", needle = "leeto"
Output: -1
Explanation: "leeto" did not occur in "leetcode", so we return -1.

• C++ Solution
• Java Solution
• JavaScript Solution
• Python Solution

Find the Index of the First Occurrence in a String Leetcode Solution C++

class Solution {
public:
    int strStr(string haystack, string needle) {
        int m = haystack.size(), n = needle.size();
        for (int i = 0; i <= m - n; i++) {
            int j = 0;
            for (; j < n; j++) {
                if (haystack[i + j] != needle[j]) {
                    break;
                }
            }
            if (j == n) {
                return i;
            }
        }
        return -1;        
    }
};
Code language: C++ (cpp)

Find the Index of the First Occurrence in a String Leetcode Solution Java

class Solution {
    public int strStr(String haystack, String needle) {
        int l1 = haystack.length(), l2 = needle.length();
        if (l1 < l2) {
            return -1;
        } else if (l2 == 0) {
            return 0;
        }
        int threshold = l1 - l2;
        for (int i = 0; i <= threshold; ++i) {
            if (haystack.substring(i,i+l2).equals(needle)) {
                return i;
            }
        }
        return -1;
    }
}
Code language: Java (java)

Find the Index of the First Occurrence in a String Leetcode Solution JavaScript

var strStr = function(haystack, needle) {
    if (needle.length == 0) return 0;
    for (let i = 0; i < haystack.length; i++) {
        let k = i, j = 0;
        while (haystack[k] == needle[j] && j < needle.length) {
            k++, j++;
        }
        if (j == needle.length) return i;
    }
    return -1;     
};
Code language: JavaScript (javascript)

Find the Index of the First Occurrence in a String Leetcode Solution Python

class Solution(object):
    def strStr(self, haystack, needle):
        for i in range(len(haystack) - len(needle)+1):
            if haystack[i:i+len(needle)] == needle:
                return i
        return -1
Code language: Python (python)