Verify/level_ancestor.test.cpp

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Last update: 2020-11-05 12:15:41+09:00
Problem: https://judge.yosupo.jp/problem/lca

Depends on

Code

#define PROBLEM "https://judge.yosupo.jp/problem/lca"

#include "../Graph/level_ancestor.hpp"

#include <iostream>

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    int n, q;
    std::cin >> n >> q;

    Graph<> graph(n);
    for (int v = 1; v < n; ++v) {
        int p;
        std::cin >> p;
        graph.span(false, p, v);
    }

    LevelAncestor la(graph, 0);

    while (q--) {
        int u, v;
        std::cin >> u >> v;
        std::cout << la.lca(u, v) << "\n";
    }

    return 0;
}

#line 1 "Verify/level_ancestor.test.cpp"
#define PROBLEM "https://judge.yosupo.jp/problem/lca"

#line 2 "Graph/level_ancestor.hpp"

#line 2 "Graph/graph.hpp"

#include <vector>

template <class Cost = int>
struct Edge {
    int src, dst;
    Cost cost;

    Edge() = default;
    Edge(int src, int dst, Cost cost = 1)
        : src(src), dst(dst), cost(cost){};

    bool operator<(const Edge<Cost>& e) const { return cost < e.cost; }
    bool operator>(const Edge<Cost>& e) const { return cost > e.cost; }
};

template <class Cost = int>
struct Graph : public std::vector<std::vector<Edge<Cost>>> {
    using std::vector<std::vector<Edge<Cost>>>::vector;

    void span(bool direct, int src, int dst, Cost cost = 1) {
        (*this)[src].emplace_back(src, dst, cost);
        if (!direct) (*this)[dst].emplace_back(dst, src, cost);
    }
};
#line 4 "Graph/level_ancestor.hpp"

template <class Cost = int>
struct LevelAncestor {
    Graph<Cost> tree;
    std::vector<std::vector<int>> par;
    std::vector<int> depth;
    std::vector<Cost> cdepth;
    int kmax;

    void dfs(int v, int p = -1, int d = 0, Cost c = 0) {
        par[v][0] = p;
        depth[v] = d;
        cdepth[v] = c;

        for (const auto& e : tree[v]) {
            if (e.dst == p) continue;
            dfs(e.dst, v, d + 1, c + e.cost);
        }
    }

    LevelAncestor(const Graph<Cost>& tree, int root)
        : tree(tree), par(tree.size()), depth(tree.size(), -1), cdepth(tree.size()) {
        kmax = 0;
        while ((1 << kmax) < (int)tree.size()) ++kmax;
        for (auto& v : par) v.resize(kmax + 1);

        dfs(root);

        for (int k = 1; k <= kmax; ++k) {
            for (int v = 0; v < (int)tree.size(); ++v) {
                int p = par[v][k - 1];
                par[v][k] = (p == -1 ? -1 : par[p][k - 1]);
            }
        }
    }

    int climb(int v, int d) const {
        for (int k = kmax; k >= 0 && v != -1; --k) {
            if ((1 << k) > d) continue;

            v = par[v][k];
            d -= (1 << k);
        }
        return v;
    }

    int lca(int u, int v) const {
        if (depth[u] < depth[v]) std::swap(u, v);

        if (depth[u] > depth[v]) {
            u = climb(u, depth[u] - depth[v]);
        }

        if (u == v) return u;

        for (int k = kmax; k >= 0; --k) {
            if (par[u][k] != par[v][k]) {
                u = par[u][k];
                v = par[v][k];
            }
        }
        return par[u][0];
    }

    int dist(int u, int v) const {
        int p = lca(u, v);
        return depth[u] + depth[v] - depth[p] * 2;
    }

    Cost cdist(int u, int v) const {
        int p = lca(u, v);
        return cdepth[u] + cdepth[v] - cdepth[p] * 2;
    }
};
#line 4 "Verify/level_ancestor.test.cpp"

#include <iostream>

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    int n, q;
    std::cin >> n >> q;

    Graph<> graph(n);
    for (int v = 1; v < n; ++v) {
        int p;
        std::cin >> p;
        graph.span(false, p, v);
    }

    LevelAncestor la(graph, 0);

    while (q--) {
        int u, v;
        std::cin >> u >> v;
        std::cout << la.lca(u, v) << "\n";
    }

    return 0;
}