CodeForces 609B The Best Gift

统计+枚举

#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;

int a[];

int main()
{
    int n,m;
    scanf("%d%d",&n,&m);
    memset(a,,sizeof a);
    for(int i=;i<=n;i++)
    {
        int x;
        scanf("%d",&x);
        a[x]++;
    }
    int ans=;
    for(int i=;i<=m;i++)
    {
        for(int j=i+;j<=m;j++)
        {
            ans=ans+a[i]*a[j];
        }
    }
    printf("%d\n",ans);
    return ;
}