[LeetCode]Implement strStr()

题目描述:(链接）

Implement strStr().

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

解题思路：

class Solution {
public:
int strStr(string haystack, string needle) {
int sub_len = needle.size();
int total_len = haystack.size();
if (sub_len > total_len) {
return -1;
}

if (haystack == needle) {
return 0;
}

int result = -1;
for (int i = 0; i <= total_len - sub_len; ++i) {
if (haystack.substr(i, sub_len) == needle) {
result = i;
break;
}
}

return result;
}
};