1. 使用map统计数组里面的数字的个数
2. 找出数组中任意一个重复的数字，遍历map如果发现个数大于1，则输出返回即可

1. 可能数组里没有重复的数字，返回false

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) {
        map<int, int> mark;
        map<int, int>::iterator it;
        for(int i = 0; i < length; i++) {
             
            it = mark.find(numbers[i]);
            if (it == mark.end()) {
                mark.insert(pair<int, int>(numbers[i], 1));
            } else {
                mark[numbers[i]]++;
            }
        }
        int index = 0;
        for (it = mark.begin(); it != mark.end(); it++) {
            if (it->second > 1){
                duplication[index] = it->first;
                index++;
                return true;
            }
        }
        if (index == 0)
            return false;
        else
            return true;
    }
};