'commit'

TangDou/Topic/PrefixAndSuffix/P1719_2.cpp

@@ -1,27 +1,33 @@
 #include <bits/stdc++.h>
 using namespace std;
-const int N = 310;
-
-int a[N][N], s[N][N], dp[N];
-int n, ans;
+const int N = 125;
+int n; // 边长
+int ans = INT_MIN;
+int a[N][N]; // 记录矩形
+int s[N];    // s[k]表示[i,j]行范围内第k列的前缀和
+int dp[N];
 
+void getDp() {
+    memset(dp, 0, sizeof dp);
+    for (int i = 1; i <= n; i++) {
+        dp[i] = max(s[i], dp[i - 1] + s[i]); // 只有当前列，或者加上上前面val最大的矩形
+        ans = max(ans, dp[i]);
+    }
+}
 int main() {
     cin >> n;
     for (int i = 1; i <= n; i++)
-        for (int j = 1; j <= n; j++) {
+        for (int j = 1; j <= n; j++)
             cin >> a[i][j];
-            s[i][j] = s[i - 1][j] + a[i][j];
-        }
 
-    for (int i = 1; i <= n; i++) {
-        for (int k = 1; k <= i; k++) {
-            for (int j = 1; j <= n; j++) {
-                int gap = s[i][j] - s[i - k][j];
-                dp[j] = max(dp[j - 1] + gap, gap);
-                ans = max(dp[j], ans);
-            }
+    for (int i = 1; i <= n; i++) {       // 枚举起始行
+        memset(s, 0, sizeof s);          // 重置前缀数组
+        for (int j = i; j <= n; j++) {   // 枚举末尾行
+            for (int k = 1; k <= n; k++) // 枚举列
+                s[k] += a[j][k];
+            getDp();
         }
     }
-    cout << ans;
+    cout << ans << endl;
     return 0;
 }