rs: add «463. Island Perimeter»

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

rs/island-perimeter.rs

@@ -0,0 +1,25 @@
+struct Solution {}
+impl Solution {
+    fn indices(grid: &[Vec<i32>]) -> impl Iterator<Item = (isize, isize)> + '_ {
+        (0..grid.len()).flat_map(move |y| (0..grid[y].len()).map(move |x| (x as isize, y as isize)))
+    }
+
+    fn in_range(grid: &[Vec<i32>], y: isize, x: isize) -> bool {
+        y >= 0 && y < grid.len() as isize && x >= 0 && x < grid[y as usize].len() as isize
+    }
+
+    fn count_empty(grid: &[Vec<i32>], y: isize, x: isize) -> i32 {
+        [-1, 1]
+            .into_iter()
+            .flat_map(|d| [(x + d, y), (x, y + d)])
+            .filter(|&(x, y)| !Self::in_range(grid, y, x) || grid[y as usize][x as usize] == 0)
+            .count() as i32
+    }
+
+    pub fn island_perimeter(grid: Vec<Vec<i32>>) -> i32 {
+        Self::indices(&grid)
+            .filter(|&(x, y)| grid[y as usize][x as usize] != 0)
+            .map(|(x, y)| Self::count_empty(&grid, y, x))
+            .sum()
+    }
+}