codeforces #164 div2

http://codeforces.com/problemset/problem/268/A

http://codeforces.com/problemset/problem/268/B

http://codeforces.com/problemset/problem/268/C

// cf #164 div2  A
 #include<stdio.h>
int a[30],b[30];
int main(){
    //freopen("input.txt","r",stdin);
  //  freopen("output.txt","w",stdout);
   int  n,i,j,num=0;
   scanf("%d",&n);
   for(i=0;i<n;i++)
    scanf("%d%d",&a[i],&b[i]);
     for(i=0;i<n;i++)
    for(j=0;j<n;j++)
     if(a[i]==b[j])
        num++;
     printf("%d\n",num);
   return 0;
}

// cf #164 div2 B
// 找规律，S=n+ (n-1)+1*(n-2)+ (n-2)+2*(n-3)+ ...+ 3+(n-3)*2+ 2+(n-2)*1+1.
 #include<stdio.h>
int main(){
  int i,s,j,n;
 // freopen("input.txt","r",stdin);
  while(scanf("%d",&n)!=EOF&&n>0){
    if(n==1){
        printf("1\n"); break;
    }
   if(n==2){
    printf("3\n"); break;
}
  j=1; s=0;
  for(i=n-2;i>0;i--){
      s+=i*j;
      j++;
  }
  printf("%d\n",s+n*(n+1)/2);
}
  return 0;
}
//  cf #164 div2 c 
// 找出所有满足条件的点，x+y=min(n,m); 这条直线上的点恰好满足条件，这个算是水过的吧。

#include<stdio.h>
#include<algorithm>
#include<iostream>
using namespace std;
int n, m;
int main() {
    while (cin >> n >> m) {
        int ans = min(n, m) + 1;
        cout << ans << endl;
        for (int i = 0; i < ans; i++) {
            cout << i << " " << ans - i - 1 << endl;
        }
    }
    return 0;
}