BZOJ3732: Network(Kruskal重构树)

#include<cstdio>
#include<algorithm>
using namespace std;
const int MAXN = 1e5 + 10, INF = 1e9, B = 19;
inline int read() {
    char c = getchar(); int x = 0, f = 1;
    while(c < '0' || c > '9') {if(c == '-') f = -1; c = getchar();}
    while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
    return x * f;
}
int fa[MAXN], f[MAXN][21], ch[MAXN][2], cnt, val[MAXN], deep[MAXN];
int N, M, K;
struct Edge {
    int u, v, w;
    bool operator < (const Edge &rhs) const {
        return w < rhs.w;
    }
}E[MAXN];
int head[MAXN], num = 0;
inline void AddEdge(int x, int y, int z) {
    E[++num] = (Edge){x, y, z};
}
int find(int x) {
    if(fa[x] == x) return fa[x];
    else return fa[x] = find(fa[x]);
}
void Kruskal() {
    sort(E + 1, E + num + 1);
    int tot = 0;
    for(int i = 1; i <= M; i++) {
        int x = E[i].u, y = E[i].v;
        int fx = find(x), fy = find(y);
        if(fx == fy) continue;
        ch[++cnt][0] = fx, ch[cnt][1] = fy;
        fa[fa[x]] = fa[fa[y]] = f[fa[x]][0] = f[fa[y]][0] = cnt;
        val[cnt] = E[i].w;
        
    }
}
void dfs(int x) {
    if(!ch[x][0] && !ch[x][1]) return ;
    deep[ch[x][0]] = deep[ch[x][1]] = deep[x] + 1;
    dfs(ch[x][0]); dfs(ch[x][1]);
}
int LCA(int x, int y) {
    if(deep[x] < deep[y]) swap(x, y);
    for(int i = B; i >= 0; i--) 
        if(deep[f[x][i]] >= deep[y])
            x = f[x][i];
    if(x == y) return x;
    for(int i = B; i >= 0; i--)
        if(f[x][i] != f[y][i])
            x = f[x][i], y = f[y][i];
    return f[x][0];
}
main() {
    //freopen("a.in", "r", stdin);
    cnt = N = read(); M = read(); K = read();
    for(int i = 1; i <= N << 1; i++) fa[i] = i;
    for(int i = 1; i <= M; i++) {
        int x = read(), y = read(), z = read();
        AddEdge(x, y, z);
    }
    Kruskal();
    deep[cnt] = 1; dfs(cnt);
    for(int i = 1; i <= B; i++)
        for(int j = 1; j <= 2 * N; j++)
            f[j][i] = f[f[j][i - 1]][i - 1];
    while(K--) {
        int  x = read(), y = read();
    //    printf("%d\", LCA(x, y));
        printf("%d\n", val[LCA(x, y)]);
    }
    return 0;
}