P1565 牛宫

https://www.luogu.com.cn/record/84050544

Luogu/P1565/P1565.cpp

@@ -8,7 +8,36 @@ const char endl = '\n';
 const int N = 205;
 
 int n, m;
-long long g[N][N], ans;
+long long g[N][N], s[N][N], c[N], ans;
+
+bool check(int x) {
+    long long t = 0;
+
+    for (int i = x; i <= m; i++) {
+        t = std::min(t, c[i - x]);
+
+        if (c[i] > t) return true;
+    }
+
+    return false;
+}
+
+int calc() {
+    int l = 1, r = n, res = 0;
+
+    while (l <= r) {
+        int mid = (l + r) >> 1;
+
+        if (check(mid)) {
+            res = mid;
+            l = mid + 1;
+        } else {
+            r = mid - 1;
+        }
+    }
+
+    return res;
+}
 
 int main() {
     std::ios::sync_with_stdio(false);
@@ -20,19 +49,17 @@ int main() {
         for (int j = 1; j <= m; j++) {
             cin >> g[i][j];
 
-            g[i][j] += g[i - 1][j] + g[i][j - 1] - g[i - 1][j - 1];
+            s[i][j] = s[i - 1][j] + g[i][j];
         }
     }
 
     for (int i = 1; i <= n; i++) {
-        for (int j = 1; j <= m; j++) {
-            for (int k = i; k <= n; k++) {
-                for (int l = j; l <= m; l++) {
-                    if (g[k][l] - g[k][j - 1] - g[i - 1][l] + g[i - 1][j - 1] >= 0) {
-                        ans = std::max(ans, static_cast<long long>(k - i + 1) * (l - j + 1));
-                    }
-                }
+        for (int j = i; j <= n; j++) {
+            for (int k = 1; k <= m; k++) {
+                c[k] = c[k - 1] + s[j][k] - s[i - 1][k];
             }
+
+            ans = std::max(ans, static_cast<long long>(j - i + 1) * calc());
         }
     }