Submission #1222852

#	Time	Username	Problem	Language	Result	Execution time	Memory
1222852		fermat	Bomb (IZhO17_bomb)	C++20	100 / 100	523 ms	74368 KiB

bomb

/*
 *  let's for fixed width X find the maximum valid height Y, denote it by ans[X]. 
 *  upper bound of Y for every X is ans[1].
 *   
*/
#include <iostream>
#include <vector>
#include <algorithm>
#include <assert.h>

using namespace std;

int main() {
    int n, m, res = 0;
    cin >> n >> m;
    vector <vector <int>> a(n + 5, vector<int>(m + 5, 0));
    for (int i = 1; i <= n; i++) {
        scanf("\n");
        for (int j = 1; j <= m; j++) {
            char ch;
            scanf("%c", &ch);
            a[i][j] = ch - 48;
        }
    }
    vector <vector <int>> up(n + 5, vector<int>(m + 5, 0));
    vector <vector <int>> dn(n + 5, vector<int>(m + 5, 0));
    
    for (int j = 1; j <= m; j++) {
        for (int i = 1; i <= n; i++) {
            up[i][j] = a[i][j] ? up[i - 1][j] + 1 : 0;
        }
        for (int i = n; i >= 1; i--) {
            dn[i][j] = a[i][j] ? dn[i + 1][j] + 1 : 0;
        }
    }
    vector <int> ans(m + 5, n);
    for (int t = 0; t < 2; t++) {
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if (a[i][j])
                    ans[1] = min(ans[1], up[i][j] + dn[i][j] - 1);
            }
            for (int j = 1; j <= m; j++) {
                if (a[i][j] && !a[i][j - 1]) {
                    int min_d = n, min_u = n, k;
                    
                    for (k = j; a[i][k]; k++) {
                        min_d = min(min_d, dn[i][k]);
                        min_u = min(min_u, up[i][k]);
                        ans[k - j + 1] = min(ans[k - j + 1], min_d + min_u - 1);
                    } 
                    ans[k - j + 1] = 0;
                }
            }
        }
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j + j <= m; j++) {
                swap(a[i][j], a[i][m - j + 1]);
                swap(up[i][j], up[i][m - j + 1]);
                swap(dn[i][j], dn[i][m - j + 1]);
            }
        }
    }
    for (int i = 1; i <= m; i++) {
        ans[i] = min(ans[i], ans[i - 1]);
        res = max(res, i * ans[i]);
        //cout << i << " --> " << ans[i] << endl;
    }
    cout << res << endl;
}

Compilation message (stderr)

bomb.cpp: In function 'int main()':
bomb.cpp:18:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   18 |         scanf("\n");
      |         ~~~~~^~~~~~
bomb.cpp:21:18: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   21 |             scanf("%c", &ch);
      |             ~~~~~^~~~~~~~~~~

• Subtask 1: 100 / 100