java-algorithms-data-structures/src/problems/leetcode/ImplementStrStr.java at master · metanet/java-algorithms-data-structures · GitHub

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package problems.leetcode;

/**
 * https://leetcode.com/problems/implement-strstr/
 */
public class ImplementStrStr {

    public static void main(String[] args) {
        String haystack = "hello";
        String needle = "lok";

        System.out.println(strStr(haystack, needle));
    }

    public static int strStr(String haystack, String needle) {
        if (haystack == null || needle == null || haystack.length() < needle.length()) {
            return -1;
        } else if (needle.length() == 0) {
            return 0;
        }

        for (int i = 0; i <= haystack.length() - needle.length(); i++) {
            int j = 0;
            for (; j < needle.length(); j++) {
                if (haystack.charAt(i + j) != needle.charAt(j)) {
                    break;
                }
            }

            if (j == needle.length()) {
                return i;
            }
        }

        return -1;
    }

}