货车运输-洛谷-1967-LCA+最大生成树（kruskal（并查集））

#include<cstdio>
#include<algorithm>
#define INF 999999999
using namespace std;
inline int read()//快读 
{
    int sum = 0,p = 1;
    char ch = getchar();
    while(ch < ‘0‘ || ch > ‘9‘)
    {
        if(ch == ‘-‘)
            p = -1;
        ch = getchar();
    }
    while(ch >= ‘0‘ && ch <= ‘9‘)
    {
        (sum *= 10)+= ch - ‘0‘;
        ch = getchar();
    }
    return sum * p;
}

const int maxn = 10005,maxm = 50005;
int n,m,cnt;
int head[maxn],deep[maxn],f[maxn][25],fa[maxn],w[maxn][21];
bool vis[maxn];

struct edge1
{
    int from,to,wei;
}e1[maxm];

struct edge2
{
    int next,to,wei;
}e2[maxm*2];

bool cmp(edge1 a,edge1 b)
{
    return a.wei > b.wei;
}

int find(int o)
{
    if(o == fa[o])
        return o;
    else
        return fa[o] = find(fa[o]);
}

void add(int x,int y,int z)
{
    e2[++cnt].next = head[x];
    e2[cnt].to = y;
    e2[cnt].wei = z;
    head[x] = cnt;
}

void kruskal()
{
    sort(e1+1,e1+m+1,cmp);
    for(int i = 1;i <= n;i++)
        fa[i] = i;//并查集初始化：每个节点各为一个子树，即每个点的父节点都是他自己 
    int v,u;
    for(int i = 1;i <= m;i++)
    {
        u = find(e1[i].from);
        v = find(e1[i].to);
        if(u == v)//如果两个点已经在一个图中了，即这两个点已经有一个最大的边加入到生成树中了，那么再加进去就会生成环，所以不能加 
            continue;
        fa[u] = v;//把v加入到生成树中 
        add(e1[i].from,e1[i].to,e1[i].wei);
        add(e1[i].to,e1[i].from,e1[i].wei);//无向图，双向加边 
    }
    return;
}

void dfs(int o)
{
    vis[o] = true;
    for(int i = head[o];i;i = e2[i].next)
    {
        int to = e2[i].to;
        if(vis[to])
            continue;
        deep[to] = deep[o] + 1;
        f[to][0] = o;
        w[to][0] = e2[i].wei;
        dfs(to);
    }
}
 
int lca(int x,int y)
{
    if(find(x) != find (y))
        return -1;
    int ans = INF;
    if(deep[x] > deep[y])
        swap(x,y);
    for(int i = 20;i >= 0;i--)
        if(deep[f[y][i]] >= deep[x])
        {
            ans = min(ans,w[y][i]);
            y = f[y][i];
        }
    if(x == y)
        return ans;
    for(int i = 20;i>=0;i--)
        if(f[x][i] != f[y][i])
        {
            ans = min(ans,min(w[x][i],w[y][i]));
            x = f[x][i];
            y = f[y][i];
            
        }
    ans = min(ans,min(w[x][0], w[y][0]));
    return ans;
}

int main()
{
    n = read(),m = read();
    int x,y,z;
    for(int i = 1;i <= m;i++)
    {
        x = read(),y = read(),z = read();
        e1[i].from = x;
        e1[i].to = y;
        e1[i].wei = z;
    }
    kruskal();
    for(int i = 1;i <= n;i++)
        if(!vis[i])
        {
            deep[i] = 1;
            dfs(i);
            f[i][0] = i;
            w[i][0] = INF;
        }
    for(int i = 1;i <= 20;i++)
        for(int j = 1;j <= n;j++)
        {
            f[j][i]=f[f[j][i-1]][i-1];
            w[j][i]=min(w[j][i-1], w[f[j][i-1]][i-1]);
        }
    int q = read();
    for(int i = 1;i <= q;i++)
    {
        x = read(),y = read();
        printf("%d\n",lca(x,y));
    }
    return 0;
}