package com.helloxin.leetcode.algorithms;/** * Implement strStr(). Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. Example 1: Input: haystack = "hello", needle = "ll" Output: 2 Example 2: Input: haystack = "aaaaa", needle = "bba" Output: -1 */import java.util.regex.Matcher;import java.util.regex.Pattern;/** * create by nandiexin on 2017/12/19 **/public class Implement_strStr {    /**     * 假如使用 string 的函数     * @param haystack     * @param needle     * @return     */    public static int strStr(String haystack, String needle) {           return haystack.indexOf(needle) ;    }    /**     * 用两个for循环 去解决问题  如果字符串长了  要匹配多久呢？     * @param haystack     * @param needle     * @return     */    public static int strStr2(String haystack, String needle) {        int m = haystack.length(), n = needle.length();        if (m < n) {            return -1;        }        for (int i = 0; i <= m - n; ++i) {            int j = 0;            for (j = 0; j < n; ++j) {                if (haystack.charAt(i + j) != needle.charAt(j)){                    break;                }            }            if (j == n) {                return i;            }        }        return -1;    }    /**     * 然后就可以用正则表达式啦  当然正则这个包在leetcode是通不过的哈     * @param haystack     * @param needle     * @return     */    public static int strStr3(String haystack, String needle){        Pattern p = Pattern.compile(needle);        Matcher m = p.matcher(haystack);        while(m.find()) {           return m.start();        }        return -1;    }    public static void main(String[] args) {        System.out.println(strStr3("hello","lp"));    }}