Update find-sorted-submatrices-with-maximum-element-at-most-k.cpp

Author: kamyu104

C++/find-sorted-submatrices-with-maximum-element-at-most-k.cpp

@@ -1,8 +1,47 @@
 // Time:  O(m * n)
 // Space: O(m)
 
-// mono stack, dp
+// mono stack
 class Solution {
+public:
+    long long countSubmatrices(vector<vector<int>>& grid, int k) {
+        const auto& count = [](const auto& heights) {
+            int result = 0;
+            vector<int> stk;
+            for (int i = 0, curr = 0; i < size(heights); ++i) {
+                while (!empty(stk) && heights[stk.back()] >= heights[i]) {
+                    const int j = stk.back(); stk.pop_back();
+                    curr -= (heights[j] - heights[i]) * (j - (!empty(stk) ? stk.back() : -1));
+                }
+                stk.emplace_back(i);
+                curr += heights[i];
+                result += curr;
+            }
+            return result;
+        };
+    
+        int64_t result = 0;
+        vector<int> heights(size(grid));
+        for (int j = size(grid[0]) - 1; j >= 0; --j) {
+            for (int i = 0; i < size(grid); ++i) {
+                if (grid[i][j] > k) {
+                    heights[i] = 0;
+                } else if (j + 1 < size(grid[0]) && grid[i][j] >= grid[i][j + 1]) {
+                    ++heights[i];
+                } else {
+                    heights[i] = 1;
+                }
+            }
+            result += count(heights);
+        }
+        return result;
+    }
+};
+
+// Time:  O(m * n)
+// Space: O(m)
+// mono stack, dp
+class Solution2 {
 public:
     long long countSubmatrices(vector<vector<int>>& grid, int k) {
         const auto& count = [](const auto& heights) {