题目链接: HDU 2196 Computer
分析: 先从任意一点开始, 求出它到其它点的最大距离, 然后以该点为中心更新它的邻点,
再用被更新的点去更新邻点......依此递推 !
代码:
#include <iostream> #include <cstdio> #include <cmath> #include <cstdlib> #include <string> #include <cstring> #include <algorithm> #include <iomanip> using namespace std; const int inf = 0x7FFFFFFF; const int maxn = 11111; struct node{ int to, dix, sum; node *next; }tree[maxn<<1], *head[maxn]; int ptr, n; bool vis[maxn]; int dp[maxn],h[maxn]; void Init(){ ptr=1; memset(dp,0,sizeof(dp)); memset(vis,false,sizeof(vis)); memset(head,0,sizeof(head)); } void AddEdge(int x,int y,int s){ tree[ptr].dix=s; tree[ptr].to=y; tree[ptr].next=head[x]; head[x]=&tree[ptr++]; } void DFS(int cnt){ vis[cnt]=true; node *p=head[cnt]; while(p!=NULL){ if(vis[p->to]) { p=p->next; continue; } DFS(p->to); dp[cnt]=max(dp[cnt],dp[p->to]+p->dix); p->sum=dp[p->to]+p->dix; p=p->next; } } void Tree_Dp(int father, int son){ if(vis[son]) return ; vis[son]=true; int Max=0; node* p=head[father]; while(p!=NULL){ if(p->to!=son) Max=max(Max,p->sum); p=p->next; } p=head[son]; while(p!=NULL){ if(p->to==father){ p->sum=p->dix+Max; break; } p=p->next; } p=head[son]; while(p!=NULL){ dp[son]=max(dp[son],p->sum); Tree_Dp(son,p->to); p=p->next; } } int main(){ while(~scanf("%d",&n)&&n){ Init(); for(int i=2;i<=n;++i){ int a,b; scanf("%d%d",&a,&b); AddEdge(a,i,b); AddEdge(i,a,b); } DFS(1); ///得到1点到其它所有点的距离 memset(vis,false,sizeof(vis)); node* p=head[1]; while(p!=NULL){ ///从1的邻点开始更新 Tree_Dp(1,p->to); p=p->next; } for(int i=1;i<=n;++i) printf("%d ",dp[i]); } return 0; }