Create minimum-falling-path-sum-ii.cpp

Author: kamyu104

C++/minimum-falling-path-sum-ii.cpp

@@ -0,0 +1,31 @@
+// Time:  O(m * n)
+// Space: O(1)
+
+class Solution {
+public:
+    int minFallingPathSum(vector<vector<int>>& arr) {
+        for (int i = 1; i < arr.size(); ++i) {
+            const auto& smallest_two = nsmallest(2, arr[i - 1]);
+            for (int j = 0; j < arr[0].size(); ++j) {
+                arr[i][j] += (arr[i - 1][j] == smallest_two[0]) ? smallest_two[1] : smallest_two[0];
+            }
+        }
+        return *min_element(arr.back().cbegin(), arr.back().cend());
+    }
+
+private:
+    vector<int> nsmallest(int k, const vector<int>& arr) {
+        priority_queue<int> max_heap;
+        for (const auto& x : arr) {
+            max_heap.emplace(x);
+            if (max_heap.size() > k) {
+                max_heap.pop();
+            }
+        }
+        vector<int> result;
+        while (!max_heap.empty()) {
+            result.emplace_back(max_heap.top()); max_heap.pop();
+        }
+        return {result.crbegin(), result.crend()};
+    }
+};