HJDU 1518—— Square（DFS）

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簡單深搜~~~~

<strong>#include<iostream>#include<cstring>#include<cstdio>#include<algorithm>#include<functional>#define M 30using namespace std;int vis[M],a[M],n,flag,sum;void dfs(int s,int cur,int d){    if(cur==3||flag){        flag=1;        return ;    }    for(int i=s;i<n;++i){        if(vis[i]||(d+a[i]>sum)) continue ;        vis[i]=1;        if(d+a[i]==sum) dfs(0,cur+1,0);        else dfs(i+1,cur,d+a[i]);        if(flag) return ;        vis[i]=0;        if(d==0) break; //超強力剪枝  瞬間時間變為46MS        while(a[i]==a[i+1]) i++; //剪枝    }    return ;}int main(){    //freopen("input.txt","r",stdin);    //freopen("output.txt","w",stdout);    int t;    scanf("%d",&t);    while(t--){        cin>>n;        sum=0;        for(int i=0;i<n;++i){            scanf("%d",&a[i]);            sum+=a[i];            vis[i]=0;        }        if(sum%4){            printf("no\n");            continue;        }        sum/=4;        sort(a,a+n,greater<int>());        if(a[n-1]>sum){            printf("no\n");            continue;        }        flag=0;        dfs(0,0,0);        if(flag) printf("yes\n");        else printf("no\n");    }    return 0;}</strong>