Submission #230695

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Source Code Expand

#include <iostream>
#include <vector>
#include <cmath>

using namespace std;

const int MAX_V = 100002;
const int MAX_LOG_V = 17;
vector<int> G[MAX_V];
int root;

int parent[MAX_LOG_V][MAX_V]; 
int depth[MAX_V];

void dfs(int v, int p, int d) {
    parent[0][v] = p;
    depth[v] = d;
    for(int i = 0; i < G[v].size(); i++) {
        if(G[v][i] != p) {
            dfs(G[v][i], v, d + 1);
        }
    }
}

void init(int V) {
    dfs(root, -1, 0);
    for(int k = 0; k + 1 < MAX_LOG_V; k++) {
        for(int v = 0; v < V; v++) {
            if(parent[k][v] < 0) parent[k + 1][v] = -1;
            else parent[k + 1][v] = parent[k][parent[k][v]];
        }
    }
}

int lca(int u, int v) {
    if(depth[u] > depth[v]) swap(u, v);
    for(int k = 0; k < MAX_LOG_V; k++) {
        if((depth[v] - depth[u]) >> k & 1) {
            v = parent[k][v];
        }
        if(u == v) return u;

        for(int k = MAX_LOG_V - 1; k >= 0; k--) {
            if(parent[k][u] != parent[k][v]) {
                u = parent[k][u];
                v = parent[k][v];
            }
        }
    }
    return parent[0][u];
}

int main() {
    int n, q, a, b;
    cin >> n;
    for(int i = 0; i < n - 1; i++) {
        cin >> a >> b;
        a--, b--;
        G[a].push_back(b);
        G[b].push_back(a);
    }

    init(n);

    cin >> q;
    for(int i = 0; i < q; i++) {
        cin >> a >> b;
        a--, b--;
        int v = lca(a, b);
        cout << depth[a] + depth[b] - 2 * depth[v] + 1 << endl;
    }
}

Submission Info

Judge Result