LeetCode-Easy刷題(9) Implement strStr()

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

實現查找字符子串位置,未找到返回-1

//應該用KMP來做  
  public static int strStr(String haystack, String needle) {

        if(haystack ==null || needle ==null){
            return 0;
        }
        if(haystack.length()<needle.length() ){
            return -1;
        }
        boolean isSuccess = true;
        for (int i = 0; i <= haystack.length() - needle.length(); i++) {

            for (int j = 0; j < needle.length(); j++) {
                if(haystack.charAt(i+j)!=needle.charAt(j)){
                    isSuccess =false;
                    break;
                }
            }
            if(isSuccess){
                return i;
            }else{
                isSuccess = true;
            }
        }
        return -1;
    }