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Copy pathlca.cpp
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executable file
·77 lines (64 loc) · 1.98 KB
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#include <iostream>
#include <vector>
using namespace std;
class RMQ
{
public:
RMQ(vector<int> v) {
log_table.assign(v.size() + 1, 0);
for (int i = 2; i < log_table.size(); i++)
log_table[i] = log_table[i/2] + 1;
sparse_table.assign(log_table.back() + 1, vector<int>(v.size()));
sparse_table[0] = v;
for (int row = 1; row < sparse_table.size(); row++) {
for (int i = 0; i + (1 << row) <= v.size(); i++) {
sparse_table[row][i] = min(sparse_table[row-1][i], sparse_table[row-1][i+(1<<(row-1))]);
}
}
}
int minimum(int l, int r) {
int log = log_table[r - l];
return min(sparse_table[log][l], sparse_table[log][r - (1 << log)]);
}
private:
vector<int> log_table;
vector<vector<int>> sparse_table;
};
vector<vector<int>> adj;
vector<int> euler_tour;
vector<int> first_encounter;
vector<int> new_to_old;
void dfs_euler_tour(int v, int p) {
int new_index = new_to_old.size();
new_to_old.push_back(v);
first_encounter[v] = euler_tour.size();
euler_tour.push_back(new_index);
for (int u : adj[v]) {
if (u == p)
continue;
dfs_euler_tour(u, v);
euler_tour.push_back(new_index);
}
}
int main() {
int nodes = 10;
vector<pair<int, int>> edges = {{0, 5}, {5, 7}, {7, 2}, {5, 1}, {1, 3}, {1, 6}, {5, 8}, {0, 9}, {9, 4}};
adj.resize(nodes);
for (auto edge : edges) {
adj[edge.first].push_back(edge.second);
adj[edge.second].push_back(edge.first);
}
first_encounter.resize(nodes);
dfs_euler_tour(0, -1);
RMQ rmq(euler_tour);
int u, v;
cin >> u >> v;
int fe1 = first_encounter[u];
int fe2 = first_encounter[v];
if (fe1 > fe2)
swap(fe1, fe2);
int LCA_new_index = rmq.minimum(fe1, fe2+1);
int LCA_old_index = new_to_old[LCA_new_index];
cout << "LCA_new_index: " << LCA_new_index << endl;
cout << "LCA_old_index: " << LCA_old_index << endl;
}