028.Implement strStr()

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Solution 1: accepted 18ms

Brute force. 

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

Solution 2: accepted 58%

KMP. 

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public class Solution {
    public int strStr(String haystack, String needle) {    
        int hayLen = haystack.length(); 
        int nedLen = needle.length();   
        
        if (nedLen == 0) {
            return 0;
        }
        
        for(int i = 0; i < hayLen - nedLen + 1; i++) {
            int hay = i;
            int ned = 0;
            while (haystack.charAt(hay) == needle.charAt(ned)) {
                hay++;
                ned++;
                if (ned == nedLen)
                    return i;
                continue;
            }          
        }
        return -1;
    }
}

Neat but slower (28%) KMP. 

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public class Solution {
    public int strStr(String haystack, String needle) {          
        for(int i = 0;; i++) {
            for (int j = 0;; j++ ) {
                if (j == needle.length()) return i;
                if (i + j >= haystack.length()) return -1;
                if (haystack.charAt(i + j) != needle.charAt(j)) break;  
            }          
        }
    }
}