Submission #945074

#	Time	Username	Problem	Language	Result	Execution time	Memory
945074		atom	Bomb (IZhO17_bomb)	C++17	80 / 100	2714 ms	131072 KiB

bomb

#include "bits/stdc++.h"
// @JASPER'S BOILERPLATE
using namespace std;
using ll = long long;
 
#ifdef JASPER
#include "debug.h"
#else
#define debug(...) 166
#endif
 
signed main() {
    cin.tie(0) -> sync_with_stdio(0);
    #ifdef JASPER
        freopen("in1", "r", stdin);
    #endif
 
    int n, m;
    cin >> n >> m;
    vector <vector <int>> a(n + 5, vector <int> (m + 5, 0));
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= m; ++j) {
            char x; cin >> x;
            a[i][j] = x - '0';
        }
    }
 
    // for (int i = 1; i <= n; ++i) 
    //     for (int j = 1; j <= m; ++j)
    //         cout << a[i][j] << " \n"[j == m]; 
 
    //sub1: shortest consecutive 1ss
    if (n == 1 || m == 1) {
        if (n == 1) {
            int ans = 1e9;
            for (int i = 1; i <= m; ++i) {
                if (a[1][i] == 0) continue;
                int cur = 0;
                while (i <= m && a[1][i]) { 
                    ++cur;
                    ++i;
                }
                ans = min(ans, cur);
            }
            cout << ans << "\n";
            return 0;
        }
        if (m == 1) {
            int ans = 1e9;
            for (int i = 1; i <= n; ++i) {
                if (a[i][1] == 0) continue;
                int cur = 0;
                while (i <= n && a[i][1]) { 
                    ++cur;
                    ++i;
                }
                ans = min(ans, cur);
            }
            cout << ans << "\n";
            return 0;
        }
    }
 
    // sub3
    // if (n <= 450 && m <= 450) {
    //     vector <vector <int>> prf(n + 5, vector <int> (m + 5, 0));
    //     int earth = 0;
    //     for (int i = 1; i <= n; ++i) {
    //         for (int j = 1; j <= m; ++j) {
    //             earth += (a[i][j] == 0);
    //             prf[i][j] = prf[i][j - 1] + prf[i - 1][j] - prf[i - 1][j - 1] + a[i][j];
    //         }
    //     }
 
    //     int ans = 0;
    //     for (int x = 1; x <= n; ++x) {
    //         for (int y = 1; y <= m; ++y) {
    //             if (x * y <= ans) continue;
 
    //             // prf(l)++, prf(r + 1)--;
    //             vector <vector <int>> dmg(n + 2, vector <int> (m + 2, 0));
 
    //             for (int i = 1; i + x - 1 <= n; ++i) {
    //                 for (int j = 1; j + y - 1 <= m; ++j) {
    //                     int I = i + x - 1, J = j + y - 1;
    //                     if (prf[I][J] + prf[i - 1][j - 1] - prf[I][j - 1] - prf[i - 1][J] == x * y) {
    //                         dmg[i][j] += 1;
    //                         dmg[I + 1][j] -= 1;
    //                         dmg[i][J + 1] -= 1;
    //                         dmg[I + 1][J + 1] += 1;
    //                     }
    //                 }
    //             }
 
    //             for (int i = 1; i <= n; ++i)
    //                 for (int j = 1; j <= m; ++j)
    //                     dmg[i][j] += dmg[i - 1][j] + dmg[i][j - 1] - dmg[i - 1][j - 1];

    //             bool valid = 1;
    //             for (int i = 1; i <= n; ++i) {
    //                 for (int j = 1; j <= m; ++j) {
    //                     if (a[i][j] && !dmg[i][j])
    //                         valid = 0;
    //                 }
    //             }
    //             if (valid) ans = max(ans, x * y);
    //         }
    //     }
 
    //     cout << ans << "\n";
    //     return 0;
    // }
    


    // two pointer to optimize
    vector <vector <int>> lt(n + 5, vector <int> (m + 5, 0)), rt(n + 5, vector <int> (m + 5, 0));
    vector <int> w(n + 5, 1e9); // ans(i) : W when H = i
    int min_h = 1e9;// minimum vertical strip of 1s;

    for (int _i = 0; _i <= 1; _i++) {
        for (int i = 1; i <= n; ++i) {
            for (int j = 1; j <= m; ++j)
                a[i][j]? lt[i][j] = (lt[i][j - 1] + 1) : 0;

            for (int j = m; j >= 1; --j)
                a[i][j]? rt[i][j] = (rt[i][j + 1] + 1) : 0;

            for (int j = 1; j <= m; ++j)
                if (a[i][j]) w[1] = min(w[1], rt[i][j] + lt[i][j] - (lt[i][j] && rt[i][j]));
        }
        // find feasible height
        for (int j = 1; j <= m; ++j) {
            int k = 0; // length of consecutive 1s of current column
            int l = 1e9, r = 1e9;
            for (int i = 1; i <= n; ++i) {
                if (a[i][j]) {
                    ++k;
                    l = min(l, lt[i][j]);
                    r = min(r, rt[i][j]);
                    w[k] = min(w[k], r + l - (lt[i][j] && rt[i][j]));
                }
                else {
                    if (k) min_h = min(min_h, k);
                    l = r = 1e9;
                    k = 0;
                }
            }
        }

        for (int i = 1; i <= n / 2; ++i) {
            for (int j = 1; j <= m; ++j)
                swap(a[i][j], a[n - i + 1][j]);
        }

    }

    int ans = 0;
    for (int h = 1; h <= min_h; ++h) {
        w[h + 1] = min(w[h + 1], w[h]); // width is bounded by the minimum horizontal strip
        ans = max(ans, w[h] * h);
    }

    cout << ans << "\n";
}

• Subtask 1: 80 / 100