Leetcode: 28-implement strStr()

28. Implement strStr()

Implement the strStr() function.

Given a haystack string and a needle string, find the first position of the needle string in the haystack string (starting from 0). If it does not exist, it returns -1.

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2
Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

Problem-solving ideas

一直以来，做题有一个想法，自己认为可以做出来的方法一定会非常执着的去解。该方法采用BF的暴力匹配... 自己的方法较为复杂，需要考虑的地方也比较多，算是非常笨的方法了...

Code

class Solution {
    
    
     public static  int strStr(String haystack, String needle) {
    
    
		
		//将几个特殊情况特殊处理
        if("".equals(haystack) && "".equals(needle)){
    
    
            return 0;
        }
        if("".equals(needle)){
    
    
            return 0;
        }
        if(haystack.length() < needle.length()){
    
    
            return -1;
        }

		//字符串转成字符数组
        char[] charhays = haystack.toCharArray();
        char[] charneedle = needle.toCharArray();
		
		//比较每一位字符都相等时为true
        boolean flag =false;
		//charhays[i] == charneedle[0]记录位置
        int index = -1;
		
		//记录字串是否遍历完
        int tag = 0;
        for (int i = 0; i < charhays.length; i++) {
    
    

            if(charhays[i] == charneedle[0]){
    
    
                int k = i;
                index = i;
                for (int j = 0; j < charneedle.length; j++) {
    
    
                    if(k <charhays.length &&  charhays[k] == charneedle[j]){
    
    
                        flag = true;
                        tag ++;
                    }
                    k++;
                }
                //判断是否找到子串
                if(tag == charneedle.length){
    
    
                    return index;
                }
                //必须置为0，才能进行下次匹配
                tag = 0;
            }
        }
        return  -1;
    }
}

test