28. 实现 strStr() Implement strStr()

Implement strStr().

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

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().

 

public int strStr(String haystack, String needle) {
        if( needle == null ) return 0;
        int m = haystack.length(), n = needle.length();
        for(int i = 0; i < m - n + 1; i++){
            if( haystack.substring(i, i + n).equals(needle)) return i;
        }
        return -1;

    }

 

参考链接：

https://leetcode.com/problems/implement-strstr/

https://leetcode-cn.com/problems/implement-strstr/