Implement strStr() @LeetCode

Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

	package leetcode.simpleCoding;
	/**
	* @date Feb 8, 2014
	*
	* Test case: (1123 123) ("","") --> may OutOfBound ,("a","a") --> s1.length()- s2.length()+1 not without +1, bound check.
	* return value: haystack.subString(i) but not String.valueOf(i) ("","" will return 0).
	* take care
	*/
	public class StrStr {
	public static void main(String args[]) {
	String haystack = "a";
	String needle = "a";
	System.out.println(strStr(haystack, needle));
	}
	public static String strStr(String haystack, String needle) {
	if (haystack == null || needle == null) {
	return null;
	}
	int i,j = 0;
	for (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 haystack.substring(i);
	}
	}
	return null;
	}
	}

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