Submission #1693212

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Source Code Expand

#include<cstdio>
#include<algorithm>
using namespace std;
inline int read()
{
	int x;char c;
	while((c=getchar())<'0'||c>'9');
	for(x=c-'0';(c=getchar())>='0'&&c<='9';)x=x*10+c-'0';
	return x; 
}
#define MN 100000
struct edge{int nx,t;}e[MN*2+5];
int a[MN+5],h[MN+5],en,r[MN+5],ans;
long long s[MN+5],c[MN+5];
inline void ins(int x,int y)
{
	e[++en]=(edge){h[x],y};h[x]=en;++r[x];
	e[++en]=(edge){h[y],x};h[y]=en;++r[y];
}
void dfs(int x,int fa)
{
	if(r[x]==1){s[x]=c[x]=a[x];return;}
	for(int i=h[x];i;i=e[i].nx)if(e[i].t!=fa)
		dfs(e[i].t,x),c[x]+=c[e[i].t];
	long long j,k=0;
	for(int i=h[x];i;i=e[i].nx)if(e[i].t!=fa)
	{
		j=a[x]<c[x]?min(c[x]-a[x],min(k,s[e[i].t]>>1)):0;
		j+=a[x]<c[x]-j?min(c[x]-j-a[x],min(s[x],s[e[i].t]-(j<<1))):0;
		c[x]-=j;c[fa]-=j;k+=j;s[x]+=s[e[i].t]-(j<<1);
	}
	if(a[x]^c[x])ans=1;
}
int main()
{
	int n=read(),i;
	for(i=1;i<=n;++i)a[i]=read();
	if(n==2){puts(a[1]^a[2]?"NO":"YES");return 0;}
	for(i=1;i<n;++i)ins(read(),read());
	for(i=1;i<=n;++i)if(r[i]>1){dfs(i,0);break;}
	if(ans||s[i])while(true);
	puts(ans||s[i]?"NO":"YES");
}

Submission Info

Judge Result