rs: add “931. Minimum Falling Path Sum”

Signed-off-by: Matej Focko <me@mfocko.xyz>

rs/minimum-falling-path-sum.rs

@@ -0,0 +1,29 @@
+impl Solution {
+    fn get(matrix: &[Vec<i32>], row: isize, col: isize) -> Option<i32> {
+        let rows = matrix.len() as isize;
+        if row < 0 || row >= rows {
+            return None;
+        }
+
+        let cols = matrix[row as usize].len() as isize;
+        if col < 0 || col >= cols {
+            return None;
+        }
+
+        Some(matrix[row as usize][col as usize])
+    }
+
+    pub fn min_falling_path_sum(mut matrix: Vec<Vec<i32>>) -> i32 {
+        for row in (0..matrix.len() - 1).rev() {
+            for col in 0..matrix[row].len() {
+                matrix[row][col] += vec![-1, 0, 1]
+                    .into_iter()
+                    .filter_map(|dcol| Self::get(&matrix, row as isize + 1, col as isize + dcol))
+                    .min()
+                    .unwrap()
+            }
+        }
+
+        *matrix.first().unwrap().iter().min().unwrap()
+    }
+}