#Leetcode# 28. Implement strStr()

https://leetcode.com/problems/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

代码：

class Solution {
public:
    int strStr(string haystack, string needle) {
        int l1 = haystack.length(), l2 = needle.length();
        if(l2 > l1) return -1;
        if(needle.empty()) return 0;
        for(int i = 0; i <= l1 - l2; i ++) {
            int cnt = 0;
            for(int j = 0; j < l2; j ++) {
                if(haystack[i + j] != needle[j]) break; 
                else cnt ++;
            }
            if(cnt == l2) return i;
        }
        return -1;
    }
};