数组中重复的数字

class Solution {
public:
    // Parameters:
    //        numbers:     an array of integers
    //        length:      the length of array numbers
    //        duplication: (Output) the duplicated number in the array number
    // Return value:       true if the input is valid, and there are some duplications in the array number
    //                     otherwise false
    bool duplicate(int numbers[], int length, int* duplication) {
        if(!numbers || length <= 0)
            return false;
        
           int hashTable[length];
        for(int i = 0;i<length;i++)
            hashTable[i] = 0;
        
        for(int i = 0; i < length; i++){
            ++hashTable[numbers[i]];
        }
        
        for(int j = 0; j < length; j++){
            if(hashTable[j] > 1){
                *duplication = j;
                return true;
            }
        }
        return false;
    }
};