Submission #874466

#	Time	Username	Problem	Language	Result	Execution time	Memory
874466		The_Samurai	K-th path (IZhO11_kthpath)	C++17	100 / 100	1 ms	452 KiB

kthpath

// #pragma GCC optimize("Ofast,O3")
// #pragma GCC target("avx,avx2")
#include "bits/stdc++.h"

using namespace std;
using ll = long long;

void solve() {
    int n, m;
    cin >> n >> m;
    vector<string> a(n);
    for (string &s: a) cin >> s;
    ll k;
    cin >> k;
    vector dp(n, vector(m, 0ll));
    dp[n - 1][m - 1] = 1;
    for (int i = n - 1; i >= 0; i--) {
        for (int j = m - 1; j >= 0; j--) {
            if (i + 1 < n) dp[i][j] += dp[i + 1][j];
            if (j + 1 < m) dp[i][j] += dp[i][j + 1];
        }
    }
    string ans(n + m - 1, '#');
    set<tuple<char, int, int>> v; v.emplace(a[0][0], 0, 0);
    vector cnt(n, vector(m, 0ll)); cnt[0][0] = 1;
    for (int time = 0; time < n + m - 1; time++) {
        ll sum = 0; char ch = '#';
        for (auto [c, x, y]: v) {
            if (sum + dp[x][y] * cnt[x][y] >= k) {
                ch = c;
                break;
            }
            sum += dp[x][y] * cnt[x][y];
        }
        assert(ch != '#');
        sum = 0;
        set<tuple<char, int, int>> nw;
        for (auto [c, x, y]: v) {
            if (c > ch) break;
            if (c < ch) sum += dp[x][y] * cnt[x][y];
            else {
                if (x + 1 < n) {
                    nw.emplace(a[x + 1][y], x + 1, y);
                    cnt[x + 1][y] += cnt[x][y];
                }
                if (y + 1 < m) {
                    nw.emplace(a[x][y + 1], x, y + 1);
                    cnt[x][y + 1] += cnt[x][y];
                }
            }
        }
        k -= sum;
        ans[time] = ch;
        v = nw;
    }
    cout << ans;
}

int main() {
    cin.tie(0)->sync_with_stdio(false);
#ifdef sunnatov
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    int q = 1;
    // cin >> q;
    while (q--) {
        solve();
        cout << '\n';
    }
}

• Subtask 1: 100 / 100