LeetCode Implement strStr()

最新推荐文章于 2020-08-12 12:31:54 发布

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最新推荐文章于 2020-08-12 12:31:54 发布

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Implement strStr().

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

/**
     * 字符串haystack是否存在子串needle
     * @param haystack
     * @param needle
     * @return
     */
    public int strStr(String haystack, String needle) {
        if (haystack == null) {
            return -1;
        }
        if (needle == null || needle.length() == 0) {
            return 0;
        }
        if (needle.length() > haystack.length()) {
            return -1;
        }
        char[] source = haystack.toCharArray();
        char[] target = needle.toCharArray();
        char first = target[0];
        int max = source.length - target.length;
        for (int i = 0; i <= max; i++) {
            //寻找子串第一个字符
            if (source[i] != first) {
                while (++i <= max && source[i] != first) ;
            }
            if (i <= max) {
                int j = i + 1;
                int end = i + target.length;
                for (int k = 1; j < end && source[j] == target[k]; j++,k++);
                //匹配字符串
                if (j == end) {
                    return i;
                }
            }
        }

        return -1;
    }