【每日一题】28. Implement strStr()

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

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

class Solution {
public:
    int strStr(string haystack, string needle) {
        if (needle.empty()) return 0;
        int sizeA = haystack.size(), sizeB = needle.size();
        int idx = -1;

        for (int i=0; i<= sizeA-sizeB; i++){
            bool flag = true;
            for (int j=0; j< sizeB; j++){
                if (haystack[j+i] != needle[j]){
                    flag = false;
                    break;
                }
            }
            if (flag){
                idx = i;
                break;
            }
        }
        return idx;
    }
};