ural 1471 Tree题解

本题采用LCA离线算法来做（Tarjan + 并查集）

题目连接：http://acm.timus.ru/problem.aspx?space=1&num=1471

注意本题可能会Crash。采用Color[] = 0 1 2 的解法，而不用Parent[]限制一棵树。

某种情况下也可以用

#pragma comment(linker, "/STACK:1000000000")

不过不推荐

代码：

#include <iostream>#include <stdlib.h>#include <stdio.h>#include <string.h>using namespace std;#define max 50010#define max2 75010int parent[max];//使没向变为有向的标志int father[max];//并查集集合中的代表节点int ancestor[max];//LCA中的祖先节点int color[max];//深搜的标志int dis[max];//与根节点的距离int ran[max];//并查集森林中根节点的高度int quex[max2];//查询的xint quey[max2];//查询的yint final[max2];//两节点的祖先struct edge{int y;int w;edge * next;edge(int y1,int w1,edge * next1){y = y1;        w = w1;next = next1;}}*E[max];struct que{int y;int n;que * next;que(int y1,int n1,que * next1){y = y1;n = n1;next = next1;}}*Q[max2];void makeset(int i){father[i] = i;ran[i] = 1;}int findset(int i){if(father[i] == i){return i;}return father[i] = findset(father[i]);}int unionset(int x,int y){int a = findset(x);int b = findset(y);if(a == b){return 0;}else if(ran[a]>ran[b]){father[b] = a;ran[a]+=ran[b];}else{father[a] = b;ran[b] += ran[a];}return 0;}void lca(int u){color[u] = 1;makeset(u);ancestor[u] = u;for(edge * e = E[u]; e ;e = e->next){int v = e->y;int wtemp = e->w;if(color[v] ==0){dis[v] = dis[u] + wtemp;lca(v);unionset(u,v);ancestor[findset(u)] = u;}}color[u] = 2;for(que * q = Q[u];q;q=q->next){int v = q->y;if(color[v]==2){final[q->n] = ancestor[findset(v)];}}}int main(){#ifndef ONLINE_JUDGEfreopen("in.txt","r",stdin);#endifint n,m;memset(E,0,sizeof(E));memset(Q,0,sizeof(Q));memset(final,0,sizeof(final));scanf("%d",&n);for(int i=0;i<n-1;i++){int a,b,c;scanf("%d%d%d",&a,&b,&c);E[a] = new edge(b,c,E[a]);E[b] = new edge(a,c,E[b]);}parent[0] = -1;//lca从0开始memset(dis,0,sizeof(dis));memset(color,0,sizeof(color));scanf("%d",&m);for(int i=0;i<m;i++){int x,y;scanf("%d%d",&x,&y);quex[i] = x;quey[i] = y; Q[x] = new que(y,i,Q[x]);Q[y] = new que(x,i,Q[y]);}lca(0);for(int i=0;i<m;i++){printf("%d\n",dis[quex[i]] + dis[quey[i]] - 2 * dis[final[i]]);}return 0;}

参考资料：并查集  --  http://www.cnblogs.com/liushang0419/archive/2011/05/08/2040574.html