find your present (2) 2095

 1 //map
 2 #include <set>
 3 #include <stdio.h>
 4 using namespace std;
 5 int main()
 6 {
 7     int n,x;
 8     set <int> S;
 9     while(scanf("%d",&n),n)
10     {
11         while(n--)
12         {
13             scanf("%d",&x);
14             if(S.find(x) == S.end())    //没找到，插入
15                 S.insert(x);
16             else                        //找到了，删除
17                 S.erase(x);
18         }
19         printf("%d\n",*S.begin());
20         S.clear();
21     }
22     return 0;
23 }

 1 //排序
 2 
 3 #include <cstdio>
 4 #include <algorithm>
 5 #include <iostream>
 6 #include <cstdlib>
 7 using namespace std;
 8 
 9 long long int a[1000010]; 
10 
11 int main()
12 {
13     int n;
14     while (scanf("%d",&n) && n)
15     {
16         for (int i = 0; i<n; i++)
17             scanf("%lld",&a[i]);
18         sort(a, a+n);
19         int i;
20         for (i = 1; i<n; i++)
21         {
22             if (a[i] != a[i-1]  &&  a[i] != a[i+1])
23                 break;
24         }
25         printf("%lld\n",a[i]);
26     }
27     return 0;
28 }

 1 #include <math.h>
 2 #include <string.h>
 3 #include <algorithm>
 4 #include <stdio.h>
 5 long a[100000100];
 6 int main()
 7 {
 8 
 9     memset(a,0,sizeof(a));
10     long n;
11     while(scanf("%ld",&n)!=EOF&&n!=0)
12     {
13         long long m;
14     for(int i=0;i<n;i++)
15         {
16             scanf("%lld",&m);
17             a[m]+=1;
18         }
19     for(int i=0;i<100000100;i++)
20     {
21        if(a[i]==1)
22        {
23              printf("%lld\n",i);
24        }
25     }     
26     }
27     return 0;
28 }

 1 #include <stdio.h>
 2 int main()
 3 {
 4     int n,x,ans;
 5     while(scanf("%d",&n),n)
 6     {
 7         ans = 0;
 8         while(n--)
 9         {
10             scanf("%d",&x);
11             ans ^= x;
12         }
13         printf("%d\n",ans);
14     }
15     return 0;
16 }