LeetCode-28-Implement strStr()-E（实现字符串函数）

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本文介绍了一个高效的strStr()函数实现方法，该方法用于查找一个字符串（needle）在另一个字符串（haystack）中首次出现的位置。若找到则返回索引位置，否则返回-1。特别地，当needle为空字符串时，按约定返回0。

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().

自己写的代码：(beat 97.8%)

int strStr(string haystack, string needle) {
        if(needle.length()==0)
            return 0;
        int n=haystack.length();
        int k=needle.length();       
        for(int i=0;i<=n-k;i++){
            int offset=0;
            while(haystack[i+offset]==needle[offset]&&offset<=k-1){
                offset++;
            }
            if(offset==k)
                return i;
        }
        return -1;
    }