Duplicate Pair（异或操作）

Link：http://acm.fzu.edu.cn/problem.php?pid=1001

Problem 1001 Duplicate Pair

Accept: 4923    Submit: 23300
Time Limit: 1000 mSec    Memory Limit : 65536 KB

 Problem Description

An array of length n, with address from 1 to n inclusive, contains entries from the set {1,2,...,n-1} and there's exactly two elements with the same value. Your task is to find out the value.

 Input

Input contains several cases.
Each case includes a number n (1<n<=10^6), which is followed by n integers.
The input is ended up with the end of file.

 Output

Your must output the value for each case, one per line.

 Sample Input

21 141 2 3 2

 Sample Output

12

 Source

IBM Challenge 2004.1

AC code：

#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstdio>
using namespace std;
int n,t,tt,x,ans;
int main(){
    while(scanf("%d",&n)==1){
       t=0;
       tt=0;
       while(n--){
        scanf("%d",&x);
        t^=x;
        tt^=n;
       }
        ans=t^tt;
        printf("%d\n",ans);
    }
    return 0;
}