Submission #1756099

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Source Code Expand

#include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define REP(i, n) rep(i, 0, n)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define int long long
#define chmax(x, y) x = max(x, y)
#define chmin(x, y) x = min(x, y)
using namespace std;
typedef pair<int, int> P;
const int mod = 1000000007;
const int INF = 1e12;

const int MAX_V = 100010;
const int MAX_LOG_V = 30;
vector<int> G[MAX_V];
int root = 0;
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];    
}

signed main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    rep(i, 0, n - 1){
        int x, y;
        cin >> x >> y;
        x--; y--;
        G[x].push_back(y);
        G[y].push_back(x);
    }
    init(n);
    int q;
    cin >> q;
    rep(i, 0, q){
        int a, b;
        cin >> a >> b;
        a--; b--;
        cout << depth[a] + depth[b] - 2 * depth[lca(a, b)] + 1 << endl; 
    }
}

Submission Info

Judge Result