vijos 1048 送给圣诞夜的贺卡 dfs

题目：
https://www.vijos.org/p/1048
dfs+套路剪枝；

#include<iostream>#include<cstdio>#include<algorithm>#include<cstring>using namespace std;struct hh {int num,cost;}a[1001];struct sh {int from,to;}ma[10001];int vis[10001];bool cmp(hh a,hh b) {return a.cost > b.cost;}int max(int a,int b) {return a > b ? a : b;}int tot,ans,n;int sum[10001],pos[10001],nxt[10001],fst[10001],h[10001];void build(int f,int t){    ma[++tot]=(sh){f,t};    nxt[tot]=fst[f];    fst[f]=tot;    return;}void dfs(int x,int T){    if(T + sum[n] - sum[x-1] < ans) return;    ans=max(ans,T);    if(x>n) return;    if(!vis[x])    {        for(int i=fst[x];i;i=nxt[i]) vis[ma[i].to]++;        dfs(x+1,T+a[x].cost);        for(int i=fst[x];i;i=nxt[i]) vis[ma[i].to]--;    }    dfs(x+1,T);    return;}void solve(){    int x,y;    scanf("%d",&n);    for(int i=1;i<=n;i++) scanf("%d",&a[i].cost),a[i].num=i;    sort(a+1,a+n+1,cmp);    for(int i=1;i<=n;i++) pos[a[i].num]=i;    for(int i=1;i<=n;i++) sum[i]=sum[i-1]+a[i].cost;    while(~scanf("%d%d",&x,&y))    {        build(pos[x],pos[y]);        build(pos[y],pos[x]);    }    dfs(1,0);    cout<<ans<<'\n';    return;}int main(){    solve();    return 0;}