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/*
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
*/

class Solution {
    public int strStr(String haystack, String needle) {
        for( int i = 0; i <= haystack.length()-needle.length(); i++) {
            if(haystack.substring(i,i + needle.length()).equals(needle))
                return i;
        }
        return -1;
    }
}
// substring的用法+遍历