LeetCode 28. Implement strStr()

Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Clarification:

What should we return when needle is an empty string? This is a great question to ask during an interview.

For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().

Tips:当输入文空字符串的时候应该返回0

package cn.edu.csu;

public class ImplementStrStrSolution {

    public int strStr(String haystack, String needle) {
        /**
         * 朴素的字符串匹配
         * 依次选取源串中的子串进行匹配
         */
        int nlLen = needle.length();
        int hsLen = haystack.length();

        if (nlLen > hsLen) {
            return -1;
        }

        if (nlLen == 0 || haystack.equals(needle)) {
            return 0;
        }

        int result = -1;
        for (int i = 0; i < hsLen - nlLen + 1; i++) {

            //每次匹配不成功模块向后滑动一位
            if (haystack.substring(i, i + nlLen).equals(needle)) {
                result = i;
                break;
            }

        }
        return result;
    }
}