LeetCode力扣之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

/**
 * Created by lxw, [email protected] on 2018/3/5.
 */
public class strStr {

    public int strStr(String haystack, String needle){

        if (haystack == null || needle == null
                || haystack.length() < needle.length()){
            return -1;
        }

        if (needle.length() == 0){
            return 0;
        }

        for (int i= 0; i < haystack.length(); i++){

            if (i + needle.length() > haystack.length()){
                return -1;
            }

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

        return -1;
    }

    public static void main(String[] args){
        strStr tmp = new strStr();
        String haystack = "hello";
        String needle = "lo";
        System.out.print(tmp.strStr(haystack, needle));
    }

}