【BZOJ】【P1306】【CQOI2009】【match循环赛】【题解】【搜索+剪枝】

来源：互联网发布：升级python到2.7.5 编辑：程序博客网时间：2024/06/05 03:57

传送门：

http://www.lydsy.com/JudgeOnline/problem.php?id=1306

这道题狠狠得告诉了我一句：能剪就得剪！！！

剪枝都非常非常简单，就是得全加上

①n个队伍会打(n*(n-1))/2场比赛,枚举一个队伍赢就是另一个队伍输

②每个队伍枚举到最后一场比赛时能直接计算出来

③如果当前得分大于目标分数就return

④如果以后全赢也到不了目标分数就return

完了，全加上就7s过，蒟蒻难以想象rank1 15ms是怎样过的……

Code:

#include<cstdio>#include<iostream>#include<algorithm>#include<cstring>using namespace std;int n;int sor[9];int nowsor[9];int mp[9][9];int ans=0;bool ok(){for(int i=1;i<=n;i++)if(sor[i]!=nowsor[i])return false;return true;}inline void dfs(int a,int b){      if(a>=n){if(sor[n]==nowsor[n])ans++;return;}int i=b+1;if(i==n){int k=sor[a]-nowsor[a];if(k==0){nowsor[a]+=0;nowsor[i]+=3;mp[a][i]=0;mp[i][a]=3;if(nowsor[a]<=sor[a]&&nowsor[i]<=sor[i]&&nowsor[a]+3*(n-i)>=sor[a]&&nowsor[i]+3*(n-a)>=sor[i])dfs(a+1,a+1);nowsor[a]-=0;nowsor[i]-=3;}elseif(k==1){nowsor[a]+=1;nowsor[i]+=1;mp[a][i]=1;mp[i][a]=1;if(nowsor[a]<=sor[a]&&nowsor[i]<=sor[i]&&nowsor[a]+3*(n-i)>=sor[a]&&nowsor[i]+3*(n-a)>=sor[i])dfs(a+1,a+1);nowsor[a]-=1;nowsor[i]-=1;}elseif(k==3){nowsor[a]+=3; nowsor[i]+=0;mp[a][i]=3;   mp[i][a]=0;if(nowsor[a]<=sor[a]&&nowsor[i]<=sor[i]&&nowsor[a]+3*(n-i)>=sor[a]&&nowsor[i]+3*(n-a)>=sor[i])dfs(a+1,a+1);nowsor[a]-=3; nowsor[i]-=0;}}else{nowsor[a]+=3; nowsor[i]+=0;mp[a][i]=3;   mp[i][a]=0;if(nowsor[a]<=sor[a]&&nowsor[i]<=sor[i]&&nowsor[a]+3*(n-i)>=sor[a]&&nowsor[i]+3*(n-a)>=sor[i])dfs(a,b+1);nowsor[a]-=3; nowsor[i]-=0;nowsor[a]+=1;nowsor[i]+=1;mp[a][i]=1;mp[i][a]=1;if(nowsor[a]<=sor[a]&&nowsor[i]<=sor[i]&&nowsor[a]+3*(n-i)>=sor[a]&&nowsor[i]+3*(n-a)>=sor[i])dfs(a,b+1);nowsor[a]-=1;nowsor[i]-=1;nowsor[a]+=0;nowsor[i]+=3;mp[a][i]=0;mp[i][a]=3;if(nowsor[a]<=sor[a]&&nowsor[i]<=sor[i]&&nowsor[a]+3*(n-i)>=sor[a]&&nowsor[i]+3*(n-a)>=sor[i])dfs(a,b+1);nowsor[a]-=0;nowsor[i]-=3;}}int main(){scanf("%d",&n);for(int i=1;i<=n;i++)scanf("%d",&sor[i]);dfs(1,1);cout<<ans<<endl;return 0;}

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