zoj 3195 Design the city lca倍增

题目链接

给一棵树， m个询问， 每个询问给出3个点， 求这三个点之间的最短距离。

其实就是两两之间的最短距离加起来除2.

倍增的lca模板

#include <iostream>
#include <vector>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <queue>
#include <stack>
#include <bitset>
using namespace std;
#define pb(x) push_back(x)
#define ll long long
#define mk(x, y) make_pair(x, y)
#define lson l, m, rt<<1
#define mem(a) memset(a, 0, sizeof(a))
#define rson m+1, r, rt<<1|1
#define mem1(a) memset(a, -1, sizeof(a))
#define mem2(a) memset(a, 0x3f, sizeof(a))
#define rep(i, n, a) for(int i = a; i<n; i++)
#define fi first
#define se second
typedef pair<int, int> pll;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int mod = 1e9+7;
const int inf = 1061109567;
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
const int maxn = 1e5+5;
int head[maxn*2], num, dis[maxn], f[maxn], p[maxn][20], deep[maxn], n;
struct node
{
    int to, nextt, w;
}e[maxn*2];
void add(int u, int v, int w) {
    e[num].to = v, e[num].w = w, e[num].nextt = head[u], head[u] = num++;
}
void init() {
    num = 0;
    mem1(head);
    mem1(p);
}
void dfs(int u, int fa) {
    f[u] = fa;
    for(int i = head[u]; ~i; i = e[i].nextt) {
        int v = e[i].to;
        if(v == fa)
            continue;
        dis[v] = dis[u]+e[i].w;
        deep[v] = deep[u]+1;
        dfs(v, u);
    }
}
void lca_init()
{
    int i,j;
    for(i = 1; i<=n; i++)
        p[i][0] = f[i];
    for(j = 1; (1<<j)<=n; j++) {
        for(i = 1; i<=n; i++) {
            if(p[i][j-1] != -1)
                p[i][j] = p[p[i][j-1]][j-1];
        }
    }
}
int lca(int a,int b)
{
    int i,j;
    if(deep[a]<deep[b])
        swap(a, b);
    for(i = 0; (1<<i)<=deep[a]; i++);
        i--;
    for(j = i; j>=0; j--)
        if(deep[a]-(1<<j)>=deep[b])
            a = p[a][j];
    if(a == b)
        return a;
    for(j = i; j>=0; j--)
    {
        if(p[a][j] != -1 && p[a][j] != p[b][j])
        {
            a = p[a][j];
            b = p[b][j];
        }
    }
    return f[a];
}
int main()
{
    int x, y, m, w, z, ok = 0;
    while(cin>>n) {
        if(ok)
            puts("");
        ok = 1;
        init();
        for(int i = 0; i<n-1; i++) {
            scanf("%d%d%d", &x, &y, &w);
            add(x, y, w);
            add(y, x, w);
        }
        dfs(0, -1);
        lca_init();
        cin>>m;
        while(m--) {
            scanf("%d%d%d", &x, &y, &z);
            int ans = 0;
            ans += dis[x]+dis[y]-2*dis[lca(x,y)];
            ans += dis[x]+dis[z]-2*dis[lca(x,z)];
            ans += dis[y]+dis[z]-2*dis[lca(y,z)];
            printf("%d
", ans/2);
        }
    }
    return 0;
}