暴力——BZOJ2783/Luogu3252 [JLOI2012]树

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题面：BZOJ2783 Luogu3252
淡定地用dfs+前缀和直接水过这题
前缀和查找直接沿着树高找上去好了
是不是很暴力呢？

#include<cstdio>#include<algorithm>#include<cmath>#include<cstring>#include<iostream>#include<cstdlib>#include<queue>#include<string>#include<ctime>#include<climits>using namespace std;bool rt[100001];int n,m,nedge=0,p[100001],nex[100001],head[100001],fa[100001],s[100001],a[100001],ans=0;inline void addedge(int a,int b){p[++nedge]=b;nex[nedge]=head[a];head[a]=nedge;}inline void dfs(int x){    s[x]=s[fa[x]]+a[x];    for(int rp=fa[x];rp>-1;rp=fa[rp]){        if(s[x]-s[rp]==m)ans++;        if(s[x]-s[rp]>=m)break;    }    for(int k=head[x];k;k=nex[k])dfs(p[k]);}int main(){    scanf("%d%d",&n,&m);    for(int i=1;i<=n;i++)scanf("%d",&a[i]);    for(int i=1;i<n;i++){        int x,y;scanf("%d%d",&x,&y);addedge(x,y);        fa[y]=x;rt[y]=1;    }    fa[0]=-1;s[0]=0;    for(int i=1;i<=n;i++)if(!rt[i]){        fa[i]=0;dfs(i);    }    printf("%d",ans);    return 0;}

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