Sicily 1050. Numbers & Letters

来源：互联网发布：中国软件测评中心编辑：程序博客网时间：2024/05/17 22:07

这道题也没什么好说的，直接DFS就可以了，只是要注意一句话“The aim is to use some arithmetic on (some of) the five numbers to form the target number.”，注意黑体的some of。

代码（几乎没剪枝）：

#include <iostream>#include <cstring>using namespace std;int q,m,dest;int a[6];bool used[6];void dfs(int k){ for (int i=1; i<=5; i++) if (!used[i] && a[i]<=dest && dest-a[i]<q) { q=dest-a[i]; m=a[i]; } for (int i=1; i<=5; i++) if (!used[i]) for (int j=i+1; j<=5; j++) if (!used[j]) { int tmp=a[i]; a[i]=a[i]+a[j]; used[j]=true; dfs(k-1); used[j]=false; a[i]=tmp; a[i]=a[i]-a[j]; used[j]=true; dfs(k-1); used[j]=false; a[i]=tmp; a[i]=a[j]-a[i]; used[j]=true; dfs(k-1); used[j]=false; a[i]=tmp; a[i]=a[i]*a[j]; used[j]=true; if (k!=2 ||(k==2 && tmp>=0 && tmp<=100000)) dfs(k-1); used[j]=false; a[i]=tmp; if (a[j]!=0 && a[i]%a[j]==0) { a[i]=a[i]/a[j]; used[j]=true; dfs(k-1); used[j]=false; a[i]=tmp; } if (a[i]!=0 && a[j]%a[i]==0) { a[i]=a[j]/a[i]; used[j]=true; dfs(k-1); used[j]=false; a[i]=tmp; } }}int main(){ int cases; cin>>cases; for (int o=0; o<cases; o++) { for (int i=1; i<=5; i++) cin>>a[i]; cin>>dest; memset(used,0,sizeof(used)); q=1000; dfs(5); cout<<m<<endl; } return 0;}