Submission #1594137

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Source Code Expand

#include <bits/stdc++.h>

using namespace std;

vector<int> G[100010];
int root;

int parent[20][100010];
int depth[100010];

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) continue;
    dfs(G[v][i], v, d + 1);
  }
}

void init(int V) {
  dfs(root, -1, 0);
  for (int k = 0; k + 1 < 20; 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 < 20; k++) {
    if ((depth[v] - depth[u]) >> k & 1) {
      v = parent[k][v];
    }
  }
  if (u == v) return u;
  for (int k = 19; k >= 0; k--) {
    if (parent[k][u] != parent[k][v]) {
      u = parent[k][u];
      v = parent[k][v];
    }
  }
  return parent[0][u];
}

int main(void) {
  int n;
  cin >> n;

  for (int i = 0; i < n - 1; i++) {
    int x, y;
    cin >> x >> y;
    x--, y--;
    G[x].push_back(y);
    G[y].push_back(x);
  }

  root = 0;
  init(n);

  int q;
  cin >> q;

  vector<int> ans(q);
  for (int i = 0; i < q; i++) {
    int a, b;
    cin >> a >> b;
    a--, b--;

    int c = lca(a, b);
    ans[i] = depth[a] + depth[b] - 2 * depth[c] + 1;
  }

  for (int i = 0; i < q; i++) {
    cout << ans[i] << endl;
  }

  return 0;
}

Submission Info

Judge Result