609B - Книга - лучший подарок - CodeForces Solution

#include<bits/stdc++.h>
using namespace std;
void solve(){
    int a[20],ans=0;
	for(int i=0;i<18;i++) a[i]=0;
	int n,m; cin>>n>>m;
	for(int i=0;i<n;i++){
		int x; cin>>x;
		a[x]++;
	} 
	for(int i=1;i<=10;i++){
		for(int j=i+1;j<=10;j++){
			ans+=a[i]*a[j];
		}
	}
	cout<<ans;	
}
int main(){
	cin.tie(0);
	ios::sync_with_stdio(0);
	int tc=1; 
	while(tc--) solve();
    return 0;
}
/*
	Holy AtCoder,
	let me AC!
*/

/*  printf("                                                                          \n");
	printf("                                                                           \n");
	printf("       * * *               * * *             * * *             * * *            \n");
	printf("     *       *           *       *         *      *          *       *         \n");
	printf("    *        *          *         *       *        *        *        *        \n");
	printf("            *           *         *                *                *      \n");
	printf("           *            *         *               *               *     \n");
	printf("          *             *         *              *                  *       \n");
	printf("         *              *         *             *                    *            \n");
	printf("        *               *         *           *                      *            \n");
	printf("      *                  *       *          *                *      *              \n");
	printf("    * * * * * * *          * * *          * * * * * * *        * * *   \n");                      \n");
*/