feat: add Minimum Falling Path Sum (#1182)

Co-authored-by: David Leal <halfpacho@gmail.com>

leetcode/DIRECTORY.md

@@ -100,6 +100,7 @@
 | 901  | [Online Stock Span](https://leetcode.com/problems/online-stock-span/)                                                           | [C](./src/901.c)  | Medium     |
 | 905  | [Sort Array By Parity](https://leetcode.com/problems/sort-array-by-parity/)                                                     | [C](./src/905.c)  | Easy       |
 | 917  | [Reverse Only Letters](https://leetcode.com/problems/reverse-only-letters/)                                                     | [C](./src/917.c)  | Easy       |
+| 931  | [Minimum Falling Path Sum](https://leetcode.com/problems/minimum-falling-path-sum/description/)                                 | [C](./src/931.c)  | Medium     |
 | 938  | [Range Sum of BST](https://leetcode.com/problems/range-sum-of-bst/)                                                             | [C](./src/938.c)  | Easy       |
 | 965  | [Univalued Binary Tree](https://leetcode.com/problems/univalued-binary-tree/)                                                   | [C](./src/965.c)  | Easy       |
 | 977  | [Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array/)                                           | [C](./src/977.c)  | Easy       |

leetcode/src/931.c

@@ -0,0 +1,37 @@
+#define min(a,b) (((a)<(b))?(a):(b))
+
+// Dynamic programming.
+// Runtime O(n*n)
+// Space O(n)
+int minFallingPathSum(int** matrix, int matrixSize, int* matrixColSize){
+    int* dp = calloc(matrixSize, sizeof(int));
+
+    for (int i = 0; i < matrixSize; i++){
+        int* nextDp = calloc(matrixSize, sizeof(int));
+
+        for (int j = 0; j < matrixSize; j++){
+            nextDp[j] = dp[j] + matrix[i][j];
+
+            // If not the first column - try to find minimum in prev column
+            if(j > 0){
+                nextDp[j] = min(nextDp[j], dp[j - 1] + matrix[i][j]);
+            }
+
+            // If not the last column - try to find minimum in next column
+            if (j < matrixSize - 1){
+                nextDp[j] = min(nextDp[j], dp[j + 1] + matrix[i][j]);
+            }
+        }
+
+        free(dp);
+        dp = nextDp;
+    }
+
+    int result = dp[0];
+    for (int j = 1; j < matrixSize; j++){
+        result = min(result, dp[j]);
+    }
+
+    free(dp);
+    return result;
+}