Submission #1453846

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Source Code Expand

#include <cstdio>
#include <vector>
#include <algorithm>
#include <array>
#include <set>
#include <map>
#include <queue>
#include <tuple>
#include <unordered_set>
#include <unordered_map>
#include <functional>
#include <cassert>
#define repeat(i, n) for (int i = 0; (i) < int(n); ++(i))
#define whole(f, x, ...) ([&](decltype((x)) whole) { return (f)(begin(whole), end(whole), ## __VA_ARGS__); })(x)
using ll = long long;
using namespace std;
template <class T> inline void setmin(T & a, T const & b) { a = min(a, b); }

template <typename UnaryPredicate>
ll binsearch(ll l, ll r, UnaryPredicate p) { // [l, r), p is monotone
    assert (l < r);
    -- l;
    while (r - l > 1) {
        ll m = (l + r) / 2;
        (p(m) ? r : l) = m;
    }
    return r; // = min { x in [l, r) | p(x) }, or r
}

bool pred(vector<vector<pair<int, int> > > const & g, ll limit) {
    function<vector<pair<ll, ll> > (int, int)> dfs = [&](int i, int parent) {
        if (g[i].size() == 1) {
            vector<pair<ll, ll> > result;
            result.emplace_back(0, 0);
            return result;
        }
        vector<pair<ll, ll> > left, right;
        for (auto edge : g[i]) {
            int j, value; tie(j, value) = edge;
            if (j != parent) {
                auto x = dfs(j, i);
                auto & y = left.empty() ? left : right;
                assert (y.empty());
                y = move(x);
                for (int i = 0; i < y.size(); ++ i) {
                    y[i].first  += value;
                    y[i].second += value;
                    if (y[i].first > limit or y[i].second > limit) {
                        swap(y[i], y[y.size() - 1]);
                        y.pop_back();
                        -- i;
                    }
                }
            }
        }
        vector<pair<ll, ll> > result;
        if (left.size() < right.size()) {
            left.swap(right);
        }
        for (auto l : left) {
            ll l1, l2; tie(l1, l2) = l;
            for (auto r : right) {
                ll r1, r2; tie(r1, r2) = r;
                auto push = [&](ll a, ll b, ll c) {
                    if (c <= limit) {
                        if (a < b) swap(a, b);
                        result.emplace_back(a, b);
                    }
                };
                push(l1, r1, l2 + r2);
                push(l1, r2, l2 + r1);
                push(l2, r1, l1 + r2);
                push(l2, r2, l1 + r1);
            }
        }
        whole(sort, result);
        result.erase(whole(unique, result, [&](auto x, auto y) { return x.second <= y.second; }), result.end());
        return result;
    };
    return not dfs(0, -1).empty();
}

constexpr ll inf = ll(1e18)+9;
int main() {
    int n; scanf("%d", &n);
    vector<vector<pair<int, int> > > g(n);
    repeat (i, n - 1) {
        int a, v; scanf("%d%d", &a, &v);
        g[a - 1].emplace_back(i + 1, v);
        g[i + 1].emplace_back(a - 1, v);
    }
    ll result = binsearch(0, inf, [&](ll limit) {
        return pred(g, limit);
    });
    printf("%lld\n", result);
    return 0;
}

Submission Info

Judge Result