数组中重复的数字

public class Solution {
    // Parameters:
    //    numbers:     an array of integers
    //    length:      the length of array numbers
    //    duplication: (Output) the duplicated number in the array number,length of duplication array is 1,so using duplication[0] = ? in implementation;
    //                  Here duplication like pointor in C/C++, duplication[0] equal *duplication in C/C++
    //    这里要特别注意~返回任意重复的一个，赋值duplication[0]
    // Return value:       true if the input is valid, and there are some duplications in the array number
    //                     otherwise false
    public boolean duplicate(int numbers[],int length,int [] duplication) {
        if(length == 0) return false;
        for(int i = 0; i < length; i++) {
            int index = numbers[i];
            if(index < 0) {
                index = numbers[i] + length;
            }
            if(numbers[index] < 0){
                duplication[0] = index;
                return true;
            }
            numbers[index] -= length;
        }
        return false;
    }
}