'commit'

TangDou/Topic/PrefixAndSuffix/P1719_1.cpp

@@ -0,0 +1,32 @@
+#include <bits/stdc++.h>
+using namespace std;
+const int N = 130;
+int n;
+int a[N][N];  // 存储题目中的矩阵
+int s[N][N];  // 二维前缀和
+int qz[N][N]; // qz[i][j]指的是第i行到j的前缀和
+
+int main() {
+    cin >> n;
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= n; j++) {
+            cin >> a[i][j];
+            qz[i][j] = qz[i][j - 1] + a[i][j]; // 求前缀和
+            s[i][j] = qz[i][j] + s[i - 1][j];  // 计算s
+        }
+    }
+
+    int mx = INT_MIN; // 存储答案
+    // 遍历左上角坐标，与，右下角坐标
+    for (int x1 = 1; x1 <= n; x1++) {
+        for (int y1 = 1; y1 <= n; y1++) {
+            for (int x2 = 1; x2 <= n; x2++)
+                for (int y2 = 1; y2 <= n; y2++) {
+                    if (x2 < x1 || y2 < y1) continue;                                            // 如果左上角比右下角还要大，就不用求了，下一个
+                    mx = max(mx, s[x2][y2] + s[x1 - 1][y1 - 1] - s[x2][y1 - 1] - s[x1 - 1][y2]); // 求最大值
+                }
+        }
+    }
+    cout << mx << endl; // 输出
+    return 0;
+}

TangDou/Topic/PrefixAndSuffix/P1719_2.cpp

@@ -13,14 +13,14 @@ int main() {
 
     // O(N^3)算法
     for (int i = 1; i <= n; i++) {
-        for (int j = 0; j < i; j++) {
-            int _s = 0;
+        for (int j = 0; j < i; j++) { // 前缀和需要下标从0开始
+            int sum = 0;
             for (int k = 1; k <= n; k++) {
-                _s = max(_s, 0) + s[i][k] - s[j][k];
-                res = max(res, _s);
+                sum = max(sum, 0) + s[i][k] - s[j][k];
+                res = max(res, sum);
             }
         }
     }
-    cout << res << '\n';
+    cout << res << endl;
     return 0;
 }