Submission #907374

#	Time	Username	Problem	Language	Result	Execution time	Memory
907374		daoquanglinh2007	Bomb (IZhO17_bomb)	C++17	70 / 100	971 ms	55960 KiB

bomb

#pragma GCC optimize("Ofast")
#pragma GCC target("sse4")

#include <bits/stdc++.h>
using namespace std;
 
const int NM = 2500, inf = 1e9+7;
 
int N, M, f[NM+5][NM+5], dp[NM+5][NM+5], ans = 0, H = +inf, W = +inf;
char a[NM+5][NM+5];
 
int getf(int x, int y, int u, int v){
	return f[u][v]-f[x-1][v]-f[u][y-1]+f[x-1][y-1];
}
 
bool check(int r, int c){
	for (int i = 1; i <= N; i++)
		for (int j = 1; j <= M; j++) dp[i][j] = 0;
	
	for (int i = 1; i+r-1 <= N; i++)
		for (int j = 1; j+c-1 <= M; j++)
			if (getf(i, j, i+r-1, j+c-1) == r*c){
				dp[i+r-1][j+c-1]++;
				dp[i+r-1][j-1]--;
				dp[i-1][j+c-1]--;
				dp[i-1][j-1]++;
			}
	for (int i = N; i >= 1; i--)
		for (int j = M; j >= 1; j--){
			dp[i][j] += dp[i+1][j]+dp[i][j+1]-dp[i+1][j+1];
			if (dp[i][j] == 0 && a[i][j] == '1') return 0;
		}
	return 1;
}
 
void preprocess(){
	for (int j = 1; j <= M; j++)
		for (int i = 1; i <= N; i++){
			if (a[i][j] == '0') continue;
			int k = i;
			while (k <= N && a[k][j] == '1') k++;
			H = min(H, k-i);
			i = k-1;
		}
	for (int i = 1; i <= N; i++)
		for (int j = 1; j <= M; j++){
			if (a[i][j] == '0') continue;
			int k = j;
			while (k <= M && a[i][k] == '1') k++;
			W = min(W, k-j);
			j = k-1;
		}
}
 
int main(){
//	freopen("BOMB.inp", "r", stdin);
//	freopen("BOMB.ans", "w", stdout);
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	
	cin >> N >> M;
	for (int i = 1; i <= N; i++)
		for (int j = 1; j <= M; j++){
			cin >> a[i][j];
			if (a[i][j] == '1') f[i][j] = 1;
		}
	preprocess();
	for (int i = 1; i <= N; i++)
		for (int j = 1; j <= M; j++)
			f[i][j] += f[i-1][j]+f[i][j-1]-f[i-1][j-1];
			
	if (N <= 450 && M <= 450){
		int j = W;
		for (int i = 1; i <= H; i++){
			while (j > 0 && !check(i, j)) j--;
			ans = max(ans, i*j);
		}
		cout << ans;
		return 0;
	}
			
	int l = 1, r = W;
	while (l <= r){
		int mid = (l+r)/2;
		if (check(H, mid)){
			ans = max(ans, H*mid);
			l = mid+1;
		}
		else{
			if (H-1 > 0 && check(H-1, mid)) ans = max(ans, (H-1)*mid);
			r = mid-1;
		}
	}
	l = 1, r = H;
	while (l <= r){
		int mid = (l+r)/2;
		if (check(mid, W)){
			ans = max(ans, mid*W);
			l = mid+1;
		}
		else r = mid-1;
	}
	int j = W-1;
	for (int i = 1; i < H; i++){
		if (i*j <= ans) continue;
		while (j > 0 && !check(i, j)){
			if ((double)clock()/CLOCKS_PER_SEC > 0.95) break;
			j--;
		}
		if ((double)clock()/CLOCKS_PER_SEC > 0.95) break;
		ans = max(ans, i*j);
	}
	cout << ans;
	return 0;
}

• Subtask 1: 70 / 100