Implement strStr()

Problem

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.

Constraints:

• 1 <= haystack.length, needle.length <= 10^4
• haystack and needle consist of only lowercase English characters.

Solution

O(n * m) time complexity.

class Solution {
    public int strStr(String haystack, String needle) {
        for (var h = 0; h <= haystack.length() - needle.length(); h++) {
            var ok = true;
            for (var n = 0; n < needle.length(); n++) {
                var ch = haystack.charAt(h + n);
                var cn = needle.charAt(n);
                if (ch != cn) {
                    ok = false;
                    break;
                }
            }
            if (ok) {
                return h;
            }
        }
        return -1;
    }
}