cs: add «1765. Map of Highest Peak»

URL:	https://leetcode.com/problems/map-of-highest-peak/
Signed-off-by: Matej Focko <me@mfocko.xyz>

cs/map-of-highest-peak.cs

@@ -0,0 +1,59 @@
+using Coord = (int x, int y);
+
+public class Solution {
+    private static readonly int UNSET = -1;
+    private static readonly Coord[] DIRECTIONS = [
+        (0, 1),
+        (0, -1),
+        (1, 0),
+        (-1, 0)
+    ];
+
+    private static bool IsValid(Coord dimensions, Coord position) {
+        var (width, height) = dimensions;
+        var (x, y) = position;
+
+        return y >= 0 && y < height && x >= 0 && x < width;
+    }
+
+    public int[][] HighestPeak(int[][] isWater) {
+        var (width, height) = (isWater[0].Length, isWater.Length);
+        var map = new int[height][];
+        for (var y = 0; y < height; ++y) {
+            map[y] = new int[width];
+            Array.Fill(map[y], UNSET);
+        }
+
+        var q = new Queue<Coord>();
+        for (var y = 0; y < height; ++y) {
+            for (var x = 0; x < width; ++x) {
+                if (isWater[y][x] != 1) {
+                    continue;
+                }
+
+                q.Enqueue((x, y));
+                map[y][x] = 0;
+            }
+        }
+
+        var nextHeight = 1;
+        for (var n = q.Count; n > 0; ++nextHeight, n = q.Count) {
+            for (var i = 0; i < n; ++i) {
+                var (x, y) = q.Dequeue();
+
+                foreach (var (dx, dy) in DIRECTIONS) {
+                    var nx = x + dx;
+                    var ny = y + dy;
+                    if (!IsValid((width, height), (nx, ny)) || map[ny][nx] != -1) {
+                        continue;
+                    }
+
+                    map[ny][nx] = nextHeight;
+                    q.Enqueue((nx, ny));
+                }
+            }
+        }
+
+        return map;
+    }
+}