1 #include<stdio.h>
 2 #include<string.h>
 3 #include<iostream>
 4 #include<algorithm>
 5 #include<map>
 6 using namespace std;
 7 const int maxn=10000000;
 8 map<int,int>r;
 9 int main()
10 {
11     //printf("%d\n",0^1^2^3);
12     int n,sum,a;
13     sum=0;
14     scanf("%d",&n);
15     for(int i=1;i<=n;++i)
16     {
17         scanf("%d",&a);
18         r[a]++;
19         //printf("%d\n",r[a]);
20         if(r[a]%2)
21             sum^=a;
22         else if((r[a]-1)!=0)
23             sum^=a;
24     }
25     printf("%d\n",sum);
26     return 0;
27 }

 1 #include<stdio.h>
 2 #include<string.h>
 3 #include<iostream>
 4 #include<algorithm>
 5 #include<map>
 6 using namespace std;
 7 typedef long long ll;
 8 const int maxn=10000005;
 9 int v[maxn];
10 int main()
11 {
12     int n,sum=0;
13     scanf("%d",&n);
14     for(int i=1; i<=n; ++i)
15     {
16         scanf("%d",&v[i]);
17     }
18     //sort(v+1,v+1+n);
19     int ci=0;
20     v[0]=0;
21     for(int i=1; i<=n; ++i)
22     {
23         if(v[i]!=v[i-1])
24         {
25             if(ci!=0 && ci%2)
26                 sum^=v[i-1];
27             ci=1;
28         }
29         else ci++;
30     }
31     //printf("%d\n",ci);
32     if(ci!=0 && ci%2)
33         sum^=v[n];
34     printf("%d\n",sum);
35     return 0;
36 }

 1 #include<stdio.h>
 2 #include<string.h>
 3 #include<iostream>
 4 #include<algorithm>
 5 #include<map>
 6 using namespace std;
 7 typedef long long ll;
 8 const int maxn=10000005;
 9 int main()
10 {
11     int n,sum=0,a1,a2,b;
12     scanf("%d",&n);
13     scanf("%d",&a1);
14     b=1;
15     for(int i=2; i<=n; ++i)
16     {
17         scanf("%d",&a2);
18         if(a1==a2) ++b;
19         else
20         {
21             if(b!=0 && b%2) sum^=a1;
22             b=1;
23             a1=a2;
24         }
25     }
26     if(b!=0 && b%2) sum^=a1;
27     printf("%d\n",sum);
28     return 0;
29 }