LeetCode 28: Implement strStr()

问题描述

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

java实现

class Solution {
    
    public static int strStr(String haystack, String needle) {
        if((haystack.length()==0 &&  needle.length()!=0))
            return -1;
        if (haystack.length()==0 &&  needle.length()==0||((haystack.length()!=0 &&  needle.length()==0)))
            return 0;// "" "" 0
        if (haystack.length()<needle.length())
            return -1;

        for(int i=0;i<haystack.length();i++){
            if(  haystack.length()>=i+needle.length() &&(haystack.substring(i,i+needle.length()).equals(needle)))
                return i;

        }
        return -1;
    }
}