Submission #696346

#	Time	Username	Problem	Language	Result	Execution time	Memory
696346		jhwest2	Climbers (RMI18_climbers)	C++17	5 / 100	798 ms	431668 KiB

climbers

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef array<int, 3> P;

const int N = 5050;
const ll INF = 1e18 + 10;

int n, a[N], p;
ll dp[2 * N][2 * N];

int main() {
    cin.tie(0); ios_base::sync_with_stdio(0);
    cin >> n;
    for (int i = 1; i <= n; i++) {
        int x; cin >> x;
        if (p && a[p - 1] == x)
            continue;
        while (p >= 2 && (a[p - 2] < a[p - 1]) == (a[p - 1] < x))
            --p;
        a[p++] = x;
    }
    n = p;

    for (int i = 0; i <= 2 * n - 2; i++)
        for (int j = i; j <= 2 * n - 2; j++)
            dp[i][j] = INF;
    dp[0][2 * n - 2] = 0;

    auto go = [&](int x, int y, int tx, int ty) {
        int p = (x & 1) ? a[(y + 1) / 2] : a[x / 2];
        int nx = (x & 1) ? (tx ? x + 1 : x - 1) : (tx ? x + 2 : x - 2);
        int ny = (y & 1) ? (ty ? y - 1 : y + 1) : (ty ? y - 2 : y + 2);

        bool dx = (tx ? a[nx / 2 - 1] : a[nx / 2 + 1]) < a[nx / 2]; // true if climbing
        bool dy = (ty ? a[ny / 2 + 1] : a[ny / 2 - 1]) < a[ny / 2];

        if (dx != dy)
            return P{ -1, -1, 0 };

        if (a[nx / 2] == a[ny / 2])
            return P{ nx, ny, abs(a[nx / 2] - p) };
        if (dx == (a[nx / 2] < a[ny / 2]))
            return P{ nx, ty ? ny + 1 : ny - 1, abs(a[nx / 2] - p) };
        else
            return P{ tx ? nx - 1 : nx + 1, ny, abs(a[ny / 2] - p) };
    };
    for (int d = 2 * n - 2; d >= 1; d--) {
        for (int l = 0; l + d <= 2 * n - 2; l++) {
            int r = l + d;
            if (dp[l][r] == INF)
                continue;

            auto [x, y, d] = go(l, r, 1, 1); // alice, bob goes forward
            if (x != -1)
                dp[x][y] = min(dp[x][y], dp[l][r] + d);

            if (l != 0) {
                auto [x, y, d] = go(l, r, 0, 1); // only bob goes forward
                if (x != -1)
                    dp[x][y] = min(dp[x][y], dp[l][r] + d);
            }
            if (r != 2 * n - 2) {
                auto [x, y, d] = go(l, r, 1, 0); // only alice goes forward
                if (x != -1)
                    dp[x][y] = min(dp[x][y], dp[l][r] + d);
            }
        }
    }
    ll ans = INF;
    for (int i = 0; i < n; i++)
        ans = min(ans, dp[2 * i][2 * i]);
    cout << ans;
}

• Subtask 1: 0 / 25
• Subtask 2: 5 / 25
• Subtask 3: 0 / 50