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StrStr.java

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package Algorithms.string;

public class StrStr {

public String strStr(String haystack, String needle) {

if (haystack == null || needle == null) {

return null;

}

int len1 = haystack.length();

int len2 = needle.length();

// Pay attention. if find "pl" in "apple", then len1 = 5, len2 = 2, the

// i should <= 3.

// so it should be i <= len1 - len2;

for (int i = 0; i <= len1 - len2; i++) {

int j = 0;

for (; j < len2; j++) {

if (haystack.charAt(i + j) != needle.charAt(j)) {

break;

}

}

// j goes to the end, it means that the loop never break. That means

// found the needle.

if (j == len2) {

return haystack.substring(i);

}

}

// didn't find the needle.

return null;

}

}