POJ_1986_Distance Queries(LCA+tarjan)

Distance Queries

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Description

Farmer John‘s cows refused to run in his marathon since he chose a path much too long for their leisurely lifestyle. He therefore wants to find a path of a more reasonable length. The input to this problem consists of the same
input as in "Navigation Nightmare",followed by a line containing a single integer K, followed by K "distance queries". Each distance query is a line of input containing two integers, giving the numbers of two farms between which FJ is interested in computing
distance (measured in the length of the roads along the path between the two farms). Please answer FJ‘s distance queries as quickly as possible!

Input

* Lines 1..1+M: Same format as "Navigation Nightmare"

* Line 2+M: A single integer, K. 1 <= K <= 10,000

* Lines 3+M..2+M+K: Each line corresponds to a distance query and contains the indices of two farms.

Output

* Lines 1..K: For each distance query, output on a single line an integer giving the appropriate distance.

Sample Input

7 6
1 6 13 E
6 3 9 E
3 5 7 S
4 1 3 N
2 4 20 W
4 7 2 S
3
1 6
1 4
2 6

Sample Output

13
3
36

题意：在一棵树上，查询(u,v)最短距离。

分析：LCA+tarjan离线算法，模板题。

ps：最近写LCA用的都是数组来存边，感觉比vector好用多了~~~~~

题目链接：http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=11131

代码清单：

//#pragma comment(linker, "/STACK:102400000,102400000")
#include<set>
#include<map>
#include<cmath>
#include<queue>
#include<stack>
#include<ctime>
#include<string>
#include<cstdio>
#include<cstring>
#include<cctype>
#include<cstdlib>
#include<iostream>
#include<algorithm>
using namespace std;

typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;

const int maxn = 40000 + 5;
const int maxv = 40000 + 5;
const int maxq = 10000 + 5;

struct MAX{
    int v,d;
    MAX(){}
    MAX(int v,int d){
        this -> v = v;
        this -> d = d;
    }
};

struct Q{ int v,id,next; }quary[2*maxq];
struct e{ int v,dis,next; }graph[2*maxn];
int n,m,q;
int a,b,c;
char s[3];
int father[maxn];
bool vis[maxn];
int ans[maxq];
int color[maxn];
int depth[maxn];
int nume,numq;
int heade[maxn];
int headq[maxn];

void init(){
    for(int i=1;i<=maxn;i++) father[i]=i;
    memset(ans,-1,sizeof(ans));
    memset(color,0,sizeof(color));
    memset(depth,0,sizeof(depth));
    memset(vis,false,sizeof(vis));
    memset(graph,0,sizeof(graph));
    memset(quary,0,sizeof(quary));
    memset(heade,-1,sizeof(heade));
    memset(headq,-1,sizeof(headq));
    nume=numq=0;
}

void add_E(int u,int v,int dis){
    graph[nume].v=v;
    graph[nume].dis=dis;
    graph[nume].next=heade[u];
    heade[u]=nume++;
}

void add_Q(int u,int v,int id){
    quary[numq].v=v;
    quary[numq].id=id;
    quary[numq].next=headq[u];
    headq[u]=numq++;
}

void input(){
    for(int i=0;i<m;i++){
        scanf("%d%d%d%s",&a,&b,&c,s);
        add_E(a,b,c);
        add_E(b,a,c);
    }
    scanf("%d",&q);
    for(int i=1;i<=q;i++){
        scanf("%d%d",&a,&b);
        add_Q(a,b,i);
        add_Q(b,a,i);
    }
}

int Find(int x){ return x!=father[x] ? father[x]=Find(father[x]) : father[x]; }

void tarjan(int u){
    color[u]=1;
    vis[u]=true;
    for(int i=headq[u];i!=-1;i=quary[i].next){
        int ID=quary[i].id;
        if(ans[ID]!=-1) continue;
        int v=quary[i].v;
        if(color[v]==0) continue;
        if(color[v]==1) ans[ID]=depth[u]-depth[v];
        if(color[v]==2) ans[ID]=depth[u]+depth[v]-2*depth[Find(v)];
    }
    for(int i=heade[u];i!=-1;i=graph[i].next){
        int vv=graph[i].v;
        int dis=graph[i].dis;
        if(!vis[vv]){
            depth[vv]=depth[u]+dis;
            tarjan(vv);
            color[vv]=2;
            father[vv]=u;
        }
    }
}

void solve(){
    tarjan(1);
    for(int i=1;i<=q;i++){
        printf("%d\n",ans[i]);
    }
}

int main(){
    while(scanf("%d%d",&n,&m)!=EOF){
        init();
        input();
        solve();
    }
    return 0;
}

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