Implement_strStr --leetcode

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"));
}
}