zjut1221 表达式个数

#include<iostream>#include<string>#include<algorithm>#include<cmath>using namespace std;int main(){int sum,ans;int op;int n,m;int i,t;while(scanf("%d%d",&n,&m)){sum=1; ans=0;for(op=0;op<pow((double)2,n-1);op++){sum=1;for(i=2;i<=n;i++){t=op & (int)pow((double)2,i-2);if(t) sum+=i;else sum-=i;}if(sum==m) ans++;}if(ans) printf("%d\n",ans);else printf("NO\n");}return 0;}