noya2_Library

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:heavy_check_mark: test/tree/Rerooting_DP.test.cpp

Depends on

Code

#define PROBLEM "https://yukicoder.me/problems/no/1976"

#include "../../template/template.hpp"
#include "../../tree/rerootingdp.hpp"

int main() {
    int n; in(n);
    vector<vector<pii>> g(n);
    for (int i = 0; i < n - 1; i++) {
        int u, v; in(u, v); u--, v--;
        g[u].emplace_back(v, i);
        g[v].emplace_back(u, ~i);
    }
    auto op = [&](pii a, pii b){
        return pii(max({a.first, b.first, a.second + b.second}), max(a.second, b.second));
    };
    pii e(0,0);
    auto pute = [&](pii x, int){
        return pii(max(x.first, x.second + 1), x.second + 1);
    };
    auto putv = [&](pii e, int){
        return e;
    };
    auto dp = rerootingdp<pii,pii>(op,e,pute,putv,g);
    int ans = n;
    for (int u = 0; u < n; u++) {
        for (auto [v, eid] : g[u]) {
            int x = dp(u, v).first;
            int y = dp(v, u).first;
            ans = min(ans, max({x, y, (x + 1) / 2 + (y + 1) / 2 + 1}));
        }
    }
    out(ans);
}
#line 1 "test/tree/Rerooting_DP.test.cpp"
#define PROBLEM "https://yukicoder.me/problems/no/1976"

#line 2 "template/template.hpp"
using namespace std;

#include<bits/stdc++.h>
#line 1 "template/inout_old.hpp"
namespace noya2 {

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

template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v){
    int s = (int)v.size();
    for (int i = 0; i < s; i++) os << (i ? " " : "") << v[i];
    return os;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &v){
    for (auto &x : v) is >> x;
    return is;
}

void in() {}
template <typename T, class... U>
void in(T &t, U &...u){
    cin >> t;
    in(u...);
}

void out() { cout << "\n"; }
template <typename T, class... U, char sep = ' '>
void out(const T &t, const U &...u){
    cout << t;
    if (sizeof...(u)) cout << sep;
    out(u...);
}

template<typename T>
void out(const vector<vector<T>> &vv){
    int s = (int)vv.size();
    for (int i = 0; i < s; i++) out(vv[i]);
}

struct IoSetup {
    IoSetup(){
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(15);
        cerr << fixed << setprecision(7);
    }
} iosetup_noya2;

} // namespace noya2
#line 1 "template/const.hpp"
namespace noya2{

const int iinf = 1'000'000'007;
const long long linf = 2'000'000'000'000'000'000LL;
const long long mod998 =  998244353;
const long long mod107 = 1000000007;
const long double pi = 3.14159265358979323;
const vector<int> dx = {0,1,0,-1,1,1,-1,-1};
const vector<int> dy = {1,0,-1,0,1,-1,-1,1};
const string ALP = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const string alp = "abcdefghijklmnopqrstuvwxyz";
const string NUM = "0123456789";

void yes(){ cout << "Yes\n"; }
void no(){ cout << "No\n"; }
void YES(){ cout << "YES\n"; }
void NO(){ cout << "NO\n"; }
void yn(bool t){ t ? yes() : no(); }
void YN(bool t){ t ? YES() : NO(); }

} // namespace noya2
#line 2 "template/utils.hpp"

#line 6 "template/utils.hpp"

namespace noya2{

unsigned long long inner_binary_gcd(unsigned long long a, unsigned long long b){
    if (a == 0 || b == 0) return a + b;
    int n = __builtin_ctzll(a); a >>= n;
    int m = __builtin_ctzll(b); b >>= m;
    while (a != b) {
        int mm = __builtin_ctzll(a - b);
        bool f = a > b;
        unsigned long long c = f ? a : b;
        b = f ? b : a;
        a = (c - b) >> mm;
    }
    return a << std::min(n, m);
}

template<typename T> T gcd_fast(T a, T b){ return static_cast<T>(inner_binary_gcd(std::abs(a),std::abs(b))); }

long long sqrt_fast(long long n) {
    if (n <= 0) return 0;
    long long x = sqrt(n);
    while ((x + 1) * (x + 1) <= n) x++;
    while (x * x > n) x--;
    return x;
}

template<typename T> T floor_div(const T n, const T d) {
    assert(d != 0);
    return n / d - static_cast<T>((n ^ d) < 0 && n % d != 0);
}

template<typename T> T ceil_div(const T n, const T d) {
    assert(d != 0);
    return n / d + static_cast<T>((n ^ d) >= 0 && n % d != 0);
}

template<typename T> void uniq(std::vector<T> &v){
    std::sort(v.begin(),v.end());
    v.erase(unique(v.begin(),v.end()),v.end());
}

template <typename T, typename U> inline bool chmin(T &x, U y) { return (y < x) ? (x = y, true) : false; }

template <typename T, typename U> inline bool chmax(T &x, U y) { return (x < y) ? (x = y, true) : false; }

template<typename T> inline bool range(T l, T x, T r){ return l <= x && x < r; }

} // namespace noya2
#line 8 "template/template.hpp"

#define rep(i,n) for (int i = 0; i < (int)(n); i++)
#define repp(i,m,n) for (int i = (m); i < (int)(n); i++)
#define reb(i,n) for (int i = (int)(n-1); i >= 0; i--)
#define all(v) (v).begin(),(v).end()

using ll = long long;
using ld = long double;
using uint = unsigned int;
using ull = unsigned long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using pil = pair<int,ll>;
using pli = pair<ll,int>;

namespace noya2{

/*　~ (. _________ . /)　*/

}

using namespace noya2;


#line 2 "tree/rerootingdp.hpp"

#line 5 "tree/rerootingdp.hpp"
#include <ranges>

namespace noya2 {

// g[from] contains outgoing edges (to, edgeid(from, to))
// (E, op, e) is commutative monoid
// ~edgeid(from, to) == edgeid(to, from)
// return calculator of dp(r, v)
template<class V, class E>
auto rerootingdp(auto op, E e, auto put_edge, auto put_vertex, const std::vector<std::vector<std::pair<int, int>>> &g, int root = 0){
    struct dp {
        // dp(r, v) : root is r, dp of subtree v
        // ans[v]  = dp(v, v)
        // from[v] = dp(v, par(v))
        // to[v]   = dp(par(v), v)
        // from[root] and to[root] is undefined
        std::vector<V> ans, from, to;
        std::vector<int> down, up;
        std::vector<std::vector<int>> childs;
        bool is_in_subtree(int r, int v){
            return down[r] < down[v] && up[v] <= up[r];
        }
        V operator()(int r, int v){
            if (r == v) return ans[v];
            if (!is_in_subtree(v, r)) return to[v];
            int le = 0, ri = childs[v].size();
            while (ri - le > 1){
                int md = (le + ri) / 2;
                if (down[childs[v][md]] <= down[r]){
                    le = md;
                }
                else {
                    ri = md;
                }
            }
            return from[childs[v][le]];
        }
    };
    int n = g.size();
    std::vector<E> from(n, e), to(n, e);
    std::vector<V> dp_to(n);
    std::vector<std::vector<int>> childs(n);
    std::vector<int> down(n), up(n);
    int t = 0;
    auto dfs = [&](auto sfs, int v, int f) -> void {
        down[v] = t++;
        childs[v].reserve(g[v].size());
        for (auto [c, eid] : g[v]){
            if (c == f) continue;
            childs[v].emplace_back(c);
            sfs(sfs, c, v);
            dp_to[c] = put_vertex(to[c], c);
            to[c] = put_edge(dp_to[c], eid);
            to[v] = op(to[v], to[c]);
        }
        up[v] = t;
    };
    dfs(dfs, root, -1);
    std::vector<V> dp_ans(n), dp_from(n);
    std::vector<E> inner(n);
    auto bfs = [&](auto sfs, int v, int f) -> void {
        int sz = g[v].size();
        inner[sz] = e;
        int i = sz-1;
        for (auto [c, eid] : g[v] | std::views::reverse){
            if (c == f) continue;
            inner[i] = op(inner[i+1], to[c]);
            i--;
        }
        dp_ans[v] = put_vertex(op(inner[++i], from[v]), v);
        E rui = e;
        for (auto [c, eid] : g[v]){
            if (c == f) continue;
            dp_from[c] = put_vertex(op(op(rui, inner[++i]), from[v]), v);
            from[c] = put_edge(dp_from[c], ~eid);
            rui = op(rui, to[c]);
        }
        for (auto [c, eid] : g[v]){
            if (c == f) continue;
            sfs(sfs, c, v);
        }
    };
    bfs(bfs, root, -1);
    return dp{dp_ans, dp_from, dp_to, down, up, childs};
}

}  // namespace noya2
#line 5 "test/tree/Rerooting_DP.test.cpp"

int main() {
    int n; in(n);
    vector<vector<pii>> g(n);
    for (int i = 0; i < n - 1; i++) {
        int u, v; in(u, v); u--, v--;
        g[u].emplace_back(v, i);
        g[v].emplace_back(u, ~i);
    }
    auto op = [&](pii a, pii b){
        return pii(max({a.first, b.first, a.second + b.second}), max(a.second, b.second));
    };
    pii e(0,0);
    auto pute = [&](pii x, int){
        return pii(max(x.first, x.second + 1), x.second + 1);
    };
    auto putv = [&](pii e, int){
        return e;
    };
    auto dp = rerootingdp<pii,pii>(op,e,pute,putv,g);
    int ans = n;
    for (int u = 0; u < n; u++) {
        for (auto [v, eid] : g[u]) {
            int x = dp(u, v).first;
            int y = dp(v, u).first;
            ans = min(ans, max({x, y, (x + 1) / 2 + (y + 1) / 2 + 1}));
        }
    }
    out(ans);
}
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