hdu2196_Computer【树形dp】

树形dp？

可以吧

但我求树上最长链

以链的一端为root建树

每一个点到达的最长距离

就是这个点到达最长链的距离（可以倍增预处理）

加上到达的点向上向下的最大值（最长链预处理）

#include <cstring>
#include <cstdio>
#include <queue>
#define cle(a,b) memset(a,b,sizeof a)
#define lp(i,j,k) for(int i = j;i <= k;++i)
using namespace std;

int read () {
	char c = getchar();
	int re = 0;
	for(;c > '9' || c < '0';c = getchar());
	for(;c <= '9' && c >= '0';c = getchar())
		re = re * 10 + c - '0';
	return re;
}

int n,U,V,MAXDIS;

int fa[10010][16];
int path[10010][16];
int depth[10010];

struct edge {
	int u,v,w,next;
}e[20020];
int cnt,head[10010];

typedef pair<int,int> pii;
queue<pii>q;
int Hash[10010];
int last[10010];
int dis[10010];


void adde (int u,int v,int w) {
	e[++cnt].v = v;
	e[cnt].u = u;
	e[cnt].w = w;
	e[cnt].next = head[u];
	head[u] = cnt;
	e[++cnt].v = u;
	e[cnt].u = v;
	e[cnt].w = w;
	e[cnt].next = head[v];
	head[v] = cnt;
}

int bfs (int u,int ti) {
	q.push(make_pair(u,0));
	
	Hash[u] = ti;
	
	int re = 0,rep = 1;
	
	while(!q.empty()) {
		u = q.front().first;
		for(int i = head[u];i != -1;i = e[i].next) {
			int v = e[i].v;
			if(Hash[v] != ti) {
				Hash[v] = ti;
				if(ti == 2)
					last[v] = i;
				if(q.front().second + e[i].w > re) {
					re = q.front().second + e[i].w;
					rep = v;
				}
				q.push(make_pair(v,q.front().second + e[i].w));
			}
		}
		q.pop();
	}
	
	if(ti == 2) {
		int t = last[rep];
		last[rep] = 0;
		int DIS = MAXDIS = re;
		while(t) {
			dis[e[t].v] = re - DIS;
			DIS -= e[t].w;
			
			if(!last[e[t].u])
				dis[e[t].u] = re;
			int shit = last[e[t].u];
			last[e[t].u] = 0;
			t = shit;
		}
		depth[rep] = 1;
	}
	
	return rep;
}

void dfs (int u) {
	for(int i = head[u];i != -1;i = e[i].next) {
		int v = e[i].v;
		if(!depth[v]) {
			depth[v] = depth[u] + 1;
			fa[v][0] = u;
			path[v][0] = e[i].w;
			int t = 0;
			while(++t <= 15) {
				if(depth[v] - (1 << t) <= 0)
					break;
				fa[v][t] = fa[fa[v][t - 1]][t - 1];
				path[v][t] = path[v][t - 1] + path[fa[v][t - 1]][t - 1];
			}
			dfs(v);
		}
	}
}

int go_up (int u) {
	int re = 0;
	int t =16;
	if(dis[u] == -1) {
		while(--t > -1) {
			if(dis[fa[u][t]] == -1) {
				re += path[u][t];
				u = fa[u][t];
			}
		}
		re += path[u][0];
		u = fa[u][0];
	}
	if(dis[u] > MAXDIS - dis[u])
		re += dis[u];
	else re += MAXDIS - dis[u];
	return re;
}

int main () {
	while(scanf("%d",&n) != EOF) {
		cle(last,0);
		cnt = 0;
		cle(fa,0);
		cle(path,0);
		cle(Hash,0);
		cle(head,-1);
		cle(dis,-1);
		cle(depth,0);
		lp(i,2,n) {
			U = read();
			V = read();
			adde(i,U,V);
		}
		dfs(bfs(bfs(1,1),2));
		dis[0] = 0;
		lp(i,1,n)
			printf("%d\n",go_up(i));
	}
}