class Solution {//根堆排序，相同元素一定在一起
public:
int duplicateInArray(vector< int >& nums) {
priority_queue< int > big_heap;

    for(int i=1;i<nums.size();i++)
    {
        big_heap.push(nums[i-1]);
    }  
    while(!big_heap.empty())
    {
       int temp= big_heap.top();
       big_heap.pop();
       if(temp==big_heap.top())
       {
        return big_heap.top();
       }

else{big_heap.pop();}
}
return -1;
}
};