Leetcode Implement strStr()

Implement strStr().

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

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解题思路：

解题想法是，从haystack的第一个位置，开始逐个判断是不是子串。如果整个子串都匹配了，那么就返回，否则继续往下挪位置。

Complexity: O(mn) , m is the length of haystack, n is the length of needle

还有一个KMP解法，算法复杂度很好，但目前没研究。以后再说。

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Java code:

 public int strStr(String haystack, String needle) {
        if( haystack == null || needle == null || needle.length() == 0 ) {
             return 0;
        }
        for(int i = 0; i < haystack.length(); i++) {
            if(i + needle.length() > haystack.length()) {
                return -1;
            }
            int m = i;
            for(int j = 0; j < needle.length(); j++) {
                if(needle.charAt(j) == haystack.charAt(m)){
                    if(j == needle.length()-1) {
                        return i;
                    }
                    m++;
                }else {
                    break;
                }
            }
        }
        return -1;
    }

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Reference:

1. http://www.programcreek.com/2012/12/leetcode-implement-strstr-java/

2. http://jakeboxer.com/blog/2009/12/13/the-knuth-morris-pratt-algorithm-in-my-own-words/

3. http://www.cnblogs.com/springfor/p/3896469.html