一个数组中有一个重复的数字，O(n) 找出来

一个数组中有一个重复的数字，时间复杂度O(n)，空间复杂度O(1) 找出来

#include <iostream>
#include<stdlib.h>
using namespace std;
int main()
{
        int n = 1001;
        int *a = new int[n];
        for (int i = 0; i < n; i++)
        {
                a[i] = i+1;
        }
        a[n-1] = rand()%n;
        for (int i = 0; i < n; i++)
        {
                cout<<a[i]<<" ";
        }
        cout << endl;
        int x = 0;
        for (int i = 1; i <= n-1; i++)
        {
                x = (x ^ i);
        }
        for (int i = 0; i < n; i++)
        {
                x = x ^ a[i];
        }
        cout <<"重复的元素为："<< x << endl;
        return 0;
}