Problem 1001 Duplicate Pair

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
2
1 1
4
1 2 3 2

Sample Output
1
2

#include"stdio.h"#include"string.h"int main(){    int n;    const int maxn=1e6;    int ai[maxn+7];    int bi[maxn+7];while(scanf("%d",&n)==1){    memset(bi,0,sizeof(bi));    for(int i=0;i<n;i++)    {        scanf("%d",&ai[i]);        bi[ai[i]]++;    }    for(int i=1;i<n;i++)    {        if(bi[i]==2)        {            printf("%d\n",i);            break;        }    }}    return 0;}