28. Implement strStr()

28. 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

笨方法1：

class Solution {
    public int strStr(String haystack, String needle) {
       if(needle==""||needle==null){
           return 0;
       } 
       else return haystack.indexOf(needle);
    }
}

　　直接用indexOf

方法2：

class Solution {
    public int strStr(String haystack, String needle) {
    if (needle.isEmpty()) return 0;
    int m = haystack.length();
    int n = needle.length();
    if (n > m) return -1;
    for (int i = 0; i <= m - n; i++) {
        int j = 0;
        for (; j < n; j++) {
            if (haystack.charAt(i + j) != needle.charAt(j)) break;
        }
        if (j == n) return i;
    }
    return -1; 
    }
}