P1131 [ZJOI2007]时态同步

十年前的ZJOI真良心，n=1e6还O(n)。

#include<cstdio>#include<iostream>#include<cstring>#include<algorithm>using namespace std;#define rep(i,j,k) for(i=j;i<=k;++i)#define per(i,j,k) for(i=j;i>=k;--i)#define sqr(x) ((x)*(x))#define G getchar()#define LL long long#define pil pair<int,LL>#define mkp make_pair#define X first#define Y second#define N 1000005#define NN 10000000#define inf 1061109567#define eps 0.00001int n,rt,tot,he[N],ne[N<<1],to[N<<1];LL W[N<<1],ans;int read(){int x=0;char ch=G;while(ch<48||ch>57)ch=G;for(;ch>47&&ch<58;ch=G)x=x*10+ch-48;return x;}void add(int x,int y,LL z){to[++tot]=y;W[tot]=z;ne[tot]=he[x];he[x]=tot;}void DFS(int x,int e){int i,y,cnt=0;LL Max=0,sum=0;for(i=he[x];i;i=ne[i])if(i!=e){DFS(y=to[i],i^1);Max=max(Max,W[i]);sum+=W[i];++cnt;}ans+=Max*cnt-sum;W[e]=W[e^1]=W[e]+Max;}int main(){int i,x,y;LL z;n=read();rt=read();tot=1;rep(i,2,n){x=read();y=read();z=read();add(x,y,z);add(y,x,z);}DFS(rt,0);printf("%lld\n",ans);return 0;}