Implement strStr()

Question: 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

You may view the full question here.

Approach 1:

//Approach 1:
//Runtime: 3ms
//Memory usage: 38.5MB
class Solution {
    public int strStr(String haystack, String needle) {
        if(needle==null || needle.length()==0){
            return 0;
        }
        int size = haystack.length();
        int needleSize = needle.length();
        char lastChar = needle.charAt(needleSize-1);
        for(int i = needleSize-1; i<size; i++){
            if(lastChar==haystack.charAt(i)){
                if(haystack.substring(i+1-needleSize,i+1).equals(needle)){
                    return i+1-needleSize;
                }
            }
        }
        return -1;
    }
}

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Cheers & Chao!