test/yosupo/lca.test.cpp

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Last update: 2023-02-04 17:43:05+09:00
Problem: https://judge.yosupo.jp/problem/lca

Depends on

Code

#define PROBLEM "https://judge.yosupo.jp/problem/lca"
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
template <class T>
using V = vector<T>;
template <class T>
using VV = V<V<T>>;

template <class T>
V<T> make_vec(size_t a) {
    return V<T>(a);
}

template <class T, class... Ts>
auto make_vec(size_t a, Ts... ts) {
    return V<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (int i = m; i < (n); i++)
#define per(i, b) per2(i, 0, b)
#define per2(i, a, b) for (int i = int(b) - 1; i >= int(a); i--)
#define ALL(c) (c).begin(), (c).end()
#define SZ(x) ((int)(x).size())

constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); }

template <class T, class U>
void chmin(T& t, const U& u) {
    if (t > u) t = u;
}
template <class T, class U>
void chmax(T& t, const U& u) {
    if (t < u) t = u;
}

template <class T>
void mkuni(vector<T>& v) {
    sort(ALL(v));
    v.erase(unique(ALL(v)), end(v));
}

template <class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << "," << p.second << ")";
    return os;
}

template <class T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "{";
    rep(i, v.size()) {
        if (i) os << ",";
        os << v[i];
    }
    os << "}";
    return os;
}

#ifdef LOCAL
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << H;
    debug_out(T...);
}
#define debug(...) \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif

template <class T>
void scan(vector<T>& v, T offset = T(0)) {
    for (auto& x : v) {
        cin >> x;
        x += offset;
    }
}

template <class T>
void print(T x, int suc = 1) {
    cout << x;
    if (suc == 1)
        cout << "\n";
    else if (suc == 2)
        cout << " ";
}

template <class T>
void print(const vector<T>& v, int suc = 1) {
    for (int i = 0; i < v.size(); ++i)
        print(v[i], i == int(v.size()) - 1 ? suc : 2);
}

struct prepare_io {
    prepare_io() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(10);
    }
} prep_io;

#define call_from_test
#include "../../cpp_src/graph/GraphBase.hpp"
#include "../../cpp_src/graph/LCA.hpp"
#undef call_from_test

int main() {
    int N, Q;
    scanf("%d %d", &N, &Q);
    V<int> p(N);
    Graph<int> g(N);
    for (int i = 1; i < N; ++i) {
        scanf("%d", &p[i]);
        g.add_edge(p[i], i);
    }
    LCA<int> lca(g, 0);
    while (Q--) {
        int a, b;
        scanf("%d %d", &a, &b);
        int v = lca.query(a, b);
        printf("%d\n", v);
    }
    return 0;
}

#line 1 "test/yosupo/lca.test.cpp"
#define PROBLEM "https://judge.yosupo.jp/problem/lca"
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
template <class T>
using V = vector<T>;
template <class T>
using VV = V<V<T>>;

template <class T>
V<T> make_vec(size_t a) {
    return V<T>(a);
}

template <class T, class... Ts>
auto make_vec(size_t a, Ts... ts) {
    return V<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (int i = m; i < (n); i++)
#define per(i, b) per2(i, 0, b)
#define per2(i, a, b) for (int i = int(b) - 1; i >= int(a); i--)
#define ALL(c) (c).begin(), (c).end()
#define SZ(x) ((int)(x).size())

constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); }

template <class T, class U>
void chmin(T& t, const U& u) {
    if (t > u) t = u;
}
template <class T, class U>
void chmax(T& t, const U& u) {
    if (t < u) t = u;
}

template <class T>
void mkuni(vector<T>& v) {
    sort(ALL(v));
    v.erase(unique(ALL(v)), end(v));
}

template <class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << "," << p.second << ")";
    return os;
}

template <class T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "{";
    rep(i, v.size()) {
        if (i) os << ",";
        os << v[i];
    }
    os << "}";
    return os;
}

#ifdef LOCAL
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << H;
    debug_out(T...);
}
#define debug(...) \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif

template <class T>
void scan(vector<T>& v, T offset = T(0)) {
    for (auto& x : v) {
        cin >> x;
        x += offset;
    }
}

template <class T>
void print(T x, int suc = 1) {
    cout << x;
    if (suc == 1)
        cout << "\n";
    else if (suc == 2)
        cout << " ";
}

template <class T>
void print(const vector<T>& v, int suc = 1) {
    for (int i = 0; i < v.size(); ++i)
        print(v[i], i == int(v.size()) - 1 ? suc : 2);
}

struct prepare_io {
    prepare_io() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(10);
    }
} prep_io;

#define call_from_test
#line 1 "cpp_src/graph/GraphBase.hpp"
template <class T>
class Edge {
   public:
    int from, to, idx;
    T cost;

    Edge() = default;
    Edge(int from, int to, T cost = T(1), int idx = -1)
        : from(from), to(to), cost(cost), idx(idx) {}
    operator int() const { return to; }

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

template <class T>
class Graph {
   public:
    using E = Edge<T>;
    vector<vector<E>> g;
    vector<E> edges;
    int es;

    Graph() {}
    Graph(int n) : g(n), edges(0), es(0){};

    int size() const { return g.size(); }

    virtual void add_directed_edge(int from, int to, T cost = 1) {
        g[from].emplace_back(from, to, cost, es++);
    }

    virtual void add_edge(int from, int to, T cost = 1) {
        g[from].emplace_back(from, to, cost, es);
        g[to].emplace_back(to, from, cost, es++);
    }

    inline vector<E>& operator[](const int& k) { return g[k]; }

    inline const vector<E>& operator[](const int& k) const {
        return g[k];
    }

    void read(int M, int offset = -1, bool directed = false,
              bool weighted = false) {
        for (int i = 0; i < M; i++) {
            int a, b;
            cin >> a >> b;
            a += offset;
            b += offset;
            T c = T(1);
            if (weighted) cin >> c;
            edges.emplace_back(a, b, c, i);
            if (directed)
                add_directed_edge(a, b, c);
            else
                add_edge(a, b, c);
        }
    }
};
#line 1 "cpp_src/graph/LCA.hpp"
template <class E>
struct LCA {
    VV<int> anc;
    V<int> dep;
    int lg;
    const Graph<E>& g;

    LCA(const Graph<E>& g, int root = 0) : g(g) {
        int n = g.size();
        lg = 1;
        while ((1 << lg) < n) lg++;
        anc = VV<int>(lg, V<int>(n, -1));
        dep = V<int>(n);
        dfs(root, -1, 0);

        for (int i = 1; i < lg; i++) {
            for (int j = 0; j < n; j++) {
                anc[i][j] =
                    (anc[i - 1][j] == -1) ? -1 : anc[i - 1][anc[i - 1][j]];
            }
        }
    }

    void dfs(int v, int p, int d) {
        anc[0][v] = p;
        dep[v] = d;
        for (auto e : g[v]) {
            if (e.to == p) continue;
            dfs(e.to, v, d + 1);
        }
    }

    int query(int u, int v) {
        if (dep[u] < dep[v]) swap(u, v);
        int df = dep[u] - dep[v];
        for (int i = lg - 1; i >= 0; --i) {
            if ((df >> i) & 1) {
                df -= (1 << i);
                u = anc[i][u];
            }
        }
        if (u == v) return u;
        for (int i = lg - 1; i >= 0; --i) {
            if (anc[i][u] != anc[i][v]) {
                u = anc[i][u];
                v = anc[i][v];
            }
        }
        return anc[0][u];
    }

    // ABC267F
    int lev_anc(int v, int k) {
        if (dep[v] < k) return -1;
        rep(i, lg) {
            if (k >> i & 1) {
                if (anc[i][v] == -1) return -1;
                v = anc[i][v];
            }
        }
        return v;
    }

    int dist(int a, int b) {
        int lc = query(a, b);
        return dep[a] + dep[b] - dep[lc] * 2;
    }
};
#line 120 "test/yosupo/lca.test.cpp"
#undef call_from_test

int main() {
    int N, Q;
    scanf("%d %d", &N, &Q);
    V<int> p(N);
    Graph<int> g(N);
    for (int i = 1; i < N; ++i) {
        scanf("%d", &p[i]);
        g.add_edge(p[i], i);
    }
    LCA<int> lca(g, 0);
    while (Q--) {
        int a, b;
        scanf("%d %d", &a, &b);
        int v = lca.query(a, b);
        printf("%d\n", v);
    }
    return 0;
}