28. Implement strStr()

Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

Clarification:

What should we return when needle is an empty string? This is a great question to ask during an interview.

For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().

Solution

class Solution {
    public int strStr(String haystack, String needle) {
        for(int i = 0;; i++) {
            for(int j = 0;; j++){
                //if it goes to the end of needle without problems
                if(j == needle.length()) return i;
                //check if we are end of haystack
                if(i+j == haystack.length()) return -1;
                //check if the char is equal
                if(haystack.charAt(i+j) != needle.charAt(j)) break;
            }
        }
    }
}

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