package codingInterview;

public class StrStr {

public static void main(String[] args) {

// TODO Auto-generated method stub

String hayStack = "hakdhgkgoodadlkg";

String needle = null;

String subString = findStr(hayStack, needle);

System.out.println(subString == null ? "not found"

: "found, subString : " + subString);

}

private static String findStr(String hayStack, String needle) {

// TODO Auto-generated method stub

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

return null;

}

int hayStackLen = hayStack.length();

int needleLen = needle.length();

if (hayStackLen == needleLen && needleLen == 0) {

return "";

}

if (needleLen == 0) {

return hayStack;

}

for (int i = 0; i < hayStackLen; i++) {

if (hayStackLen - i + 1 < needleLen) {

return null;

}

int k = i;

int j = 0;

while (j < needleLen && k < hayStackLen

&& hayStack.charAt(k) == needle.charAt(j)) {

j++;

k++;

if (j >= needleLen) {

return hayStack.substring(i);

}

}

}

return null;

}

}