HDU2586 How far away ？-白红宇

HDU2586 How far away ？

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发布时间：2019-05-25

本文共 3294 字，大约阅读时间需要 10 分钟。

Problem Description

There are n houses in the village and some bidirectional roads connecting them. Every day peole always like to ask like this "How far is it if I want to go from house A to house B"? Usually it hard to answer. But luckily int this village the answer is always unique, since the roads are built in the way that there is a unique simple path("simple" means you can't visit a place twice) between every two houses. Yout task is to answer all these curious people.

Input

First line is a single integer T(T<=10), indicating the number of test cases.

For each test case,in the first line there are two numbers n(2<=n<=40000) and m (1<=m<=200),the number of houses and the number of queries. The following n-1 lines each consisting three numbers i,j,k, separated bu a single space, meaning that there is a road connecting house i and house j,with length k(0<k<=40000).The houses are labeled from 1 to n.

Next m lines each has distinct integers i and j, you areato answer the distance between house i and house j.

Output

For each test case,output m lines. Each line represents the answer of the query. Output a bland line after each test case.

Sample Input

23 21 2 103 1 151 22 32 21 2 1001 22 1

Sample Output

1025100100

Tarjan算法：

/*//最近公共祖先题目描述：给定一棵带权树，求u，v两节点的最短长度算法思想：找到u，v两点的最近公共祖先lca(v)若dis[u]表示根节点到u的长度，则res=dis[u]+dis[v]-2*dis[lca(v)]*/#include 
   
    #include 
    
     #define NN 40002 // number of house#define MM 202   // number of queryusing namespace std;typedef struct node{    int v;//节点    int d;//v节点与nxt相连的权值    struct node *nxt;}NODE;NODE *Link1[NN];//邻接表，Link1[u]表示与u相连所有节点链NODE edg1[NN * 2]; // 树中的边NODE *Link2[NN];NODE edg2[NN * 2]; // 询问的点对int idx1, idx2, N, M;int res[MM][3]; // 记录结果，res[i][0]: u   res[i][1]: v  res[i][2]: lca(u, v)int fat[NN];//并查集表int vis[NN];//记录访问点int dis[NN];//根到i节点的长度//前插法void Add(int u, int v, int d, NODE edg[], NODE *Link[], int &idx){    edg[idx].v = v;    edg[idx].d = d;    edg[idx].nxt = Link[u];    Link[u] = edg + idx++;    edg[idx].v = u;    edg[idx].d = d;    edg[idx].nxt = Link[v];    Link[v] = edg + idx++;}int find(int x){ // 并查集路径压缩    if(x != fat[x]){        return fat[x] = find(fat[x]);    }    return x;}void Tarjan(int u){    vis[u] = 1;    fat[u] = u;    for (NODE *p = Link2[u]; p; p = p->nxt){        if(vis[p->v]){            res[p->d][2] = find(p->v); // 存的是最近公共祖先结点        }    }    for (NODE *p = Link1[u]; p; p = p->nxt){        if(!vis[p->v]){            dis[p->v] = dis[u] + p->d;            Tarjan(p->v);            fat[p->v] = u;        }    }}int main() {	freopen("C:\\in.txt","r",stdin);    int T, i, u, v, d;    scanf("%d", &T);    while(T--){        scanf("%d%d", &N, &M);        idx1 = 0;        memset(Link1, 0, sizeof(Link1));        for (i = 1; i < N; i++){            scanf("%d%d%d", &u, &v, &d);            Add(u, v, d, edg1, Link1, idx1);        }        idx2 = 0;        memset(Link2, 0, sizeof(Link2));        for (i = 1; i <= M; i++){            scanf("%d%d", &u, &v);            Add(u, v, i, edg2, Link2, idx2);            res[i][0] = u;            res[i][1] = v;        }        memset(vis, 0, sizeof(vis));        dis[1] = 0;        Tarjan(1);        for (i = 1; i <= M; i++){            printf("%d\n", dis[res[i][0]] + dis[res[i][1]] - 2 * dis[res[i][2]]);        }    }    return 0;}

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