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) {
        bool res=false;
        if(length==0) return res;
        vector<int> num(length,0);
        for(int i=0;i<length;i++)
            {
            if(numbers[i]>=0&&numbers[i]<=length-1)
                {
                num[numbers[i]]++;
                if(num[numbers[i]]>1)
                {
                    *duplication=numbers[i];
                    res=true;
                } 
            }
            else return false;
        }
        return res;
    }
};