tarjan求lca 模板

Posted 2020-12-27 wtsruvf

#include <iostream>
#include <cstdio>
#include <sstream>
#include <cstring>
#include <map>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>
#include <cmath>
#define rap(i, a, n) for(int i=a; i<=n; i++)
#define MOD 2018
#define LL long long
#define ULL unsigned long long
#define Pair pair<int, int>
#define mem(a, b) memset(a, b, sizeof(a))
#define _  ios_base::sync_with_stdio(0),cin.tie(0)
//freopen("1.txt", "r", stdin);
using namespace std;
const int maxn = 5e5 + 10, INF = 0x7fffffff;
const int maxm = 1e6 + 10;
int n, m, cnt1, cnt2, c;
int head1[maxm], head2[maxm], f[maxm], vis[maxm];
int res[maxm];

struct node
{
    int v, next;
}Node[maxm];

struct edge
{
    int v, id, next;
}Edge[maxm];

void add1_(int u, int v)
{
    Node[cnt1].v = v;
    Node[cnt1].next = head1[u];
    head1[u] = cnt1++;
}

void add1(int u, int v)
{
    add1_(u, v);
    add1_(v, u);
}

void add2_(int u, int v, int id)
{
    Edge[cnt2].v = v;
    Edge[cnt2].id = id;
    Edge[cnt2].next = head2[u];
    head2[u] = cnt2++;
}

void add2(int u, int v, int id)
{
    add2_(u, v, id);
    add2_(v, u, id);
}

int find(int x)
{
    return f[x]==x?x:(f[x] = find(f[x]));
}

int lca(int u)//把整棵树的一部分看作以节点x为根节点的小树 
{
    f[u] = u;  //由于节点u被看作是根节点，所以把u的father设为它自己 
    vis[u] = 1;  //标记为已被搜索过 
    for(int i=head1[u]; i!=-1; i=Node[i].next) //遍历所有与x相连的节点 
    {
        node e = Node[i];  //若未被搜索 
        if(vis[e.v] == -1)
        {
            lca(e.v);  //以该节点为根节点搞小树 
            f[e.v] = u; //回溯回来后更新子结点的f
        }
    }
    for(int i=head2[u]; i!=-1; i=Edge[i].next)  //搜索包含节点u的所有询问
    {
        edge e = Edge[i];
        if(vis[e.v] != -1)  //如果另一节点已被搜索过  只有另一结点被搜索过 那一条路径的f才会更新
        {
            int k = find(e.v); //寻找最近公共祖先
            res[e.id] = k; 
        }
    }
}

void init()
{
    mem(head1, -1);
    mem(head2, -1);
    mem(res, -1);
    mem(vis, -1);
    cnt1 = cnt2 = 0;
}

int main()
{
    while(scanf("%d%d%d", &n, &m, &c) != EOF)
    {
        init();
        int u, v;
        rap(i, 1, n-1)
        {
            scanf("%d%d", &u, &v);
            add1(u, v);
        }
        rap(i, 1, m)
        {
            scanf("%d%d", &u, &v);
            add2(u, v, i);
        }

        lca(c);
        rap(i, 1, m)
        {
            if(res[i] == -1) printf("Not connected
");
            else printf("%d
", res[i]);
        }
    }

    return 0;
}