74 lines
1.1 KiB
C++
74 lines
1.1 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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vector<vector<int>> bl;
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vector<vector<int>> adj;
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vector<int> depth;
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int bllog2;
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void ddfs(int o){
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for(int nv : adj[o]){
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depth[nv] = depth[o]+1;
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ddfs(nv);
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}
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}
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int lca(int a, int b){
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if(depth[a] < depth[b]) swap(a,b);
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int k = depth[a] - depth[b];
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for(int p = bllog2; p >= 0; p--){
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if(k & (1 << p)){
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a = bl[a][p];
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}
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}
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if(a == b) return a;
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for(int p = bllog2; p >= 0; p--){
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if(bl[a][p] != bl[b][p]){
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a = bl[a][p], b = bl[b][p];
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}
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}
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return bl[a][0];
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}
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int main(){
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ios::sync_with_stdio(false);
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int n,q, m, x,y;
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cin >> n;
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adj.assign(n, vector<int>());
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bllog2 = 32 - __builtin_clz(n);
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bl.assign(n, vector<int>(bllog2+1));
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bl[0][0] = 0;
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for(int i = 0; i < n; i++){
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cin >> m;
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while(m--){
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cin >> x;
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bl[x][0] = i;
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adj[i].push_back(x);
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}
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}
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for(int p = 1; p <= bllog2; p++){
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for(int i = 0; i < n; i++){
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x = bl[i][p-1];
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bl[i][p] = bl[x][p-1];
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}
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}
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depth.resize(n);
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depth[0] = 0;
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ddfs(0);
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cin >> q;
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while(q--){
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cin >> x >> y;
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cout << lca(x,y) << '\n';
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}
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return 0;
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} |