28. Implement strStr()

題目分析：

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().

代碼：

class Solution {
public:
    int strStr(string haystack, string needle) {
        if(needle == "") return 0;
        bool flag1 = false;
        int index = -1;
        for(int i = 0; i < haystack.length(); i++){
            if(haystack[i] == needle[0]){
                bool flag2 = false;
                for(int j = 1; j < needle.length(); j++){
                    if(needle[j] != haystack[i + j]){
                        flag2 = true;
                        break;
                    }
                }
                if(!flag2){
                    index = i;
                    flag1 = true;
                    break;
                }
            }
        }
        return index;
    }
};

 下雨天，沒出門，宅在宿舍刷leetcode，哈哈，今天第二道，easy題目，實現java的indexof函數，原來c中還有個strstr函數啊，新技能get。簡單粗暴，直接遍歷，找到和needle的第一個匹配的就遍歷needle。通過兩個flag來記錄是否找到。

靜心盡力！