cs: add «2503. Maximum Number of Points From Grid Queries»

URL:	https://leetcode.com/problems/maximum-number-of-points-from-grid-queries/
Signed-off-by: Matej Focko <me@mfocko.xyz>

cs/maximum-number-of-points-from-grid-queries.cs

@@ -0,0 +1,63 @@
+public class Solution {
+    private static readonly List<(int dy, int dx)> DIRECTIONS = [
+        (0, 1),
+        (0, -1),
+        (1, 0),
+        (-1, 0)
+    ];
+
+    private int[] Dijkstra(int[][] grid) {
+        var thresholds = new int[grid.Length * grid[0].Length + 1];
+
+        var minToReach = new int[grid.Length * grid[0].Length];
+        Array.Fill(minToReach, int.MaxValue);
+        minToReach[Index(0, 0)] = grid[0][0];
+
+        var q = new PriorityQueue<(int y, int x), int>();
+        q.Enqueue((0, 0), grid[0][0]);
+
+        var visited = 0;
+        while (q.TryDequeue(out var pos, out var threshold)) {
+            thresholds[++visited] = threshold;
+
+            foreach (var direction in DIRECTIONS) {
+                var y = pos.y + direction.dy;
+                var x = pos.x + direction.dx;
+
+                if (y < 0 || y >= grid.Length || x < 0 || x >= grid[y].Length || minToReach[Index(y, x)] != int.MaxValue) {
+                    continue;
+                }
+
+                minToReach[Index(y, x)] = Math.Max(threshold, grid[y][x]);
+                q.Enqueue((y, x), minToReach[Index(y, x)]);
+            }
+        }
+
+        return thresholds;
+
+        int Index(int y, int x) => y * grid[0].Length + x;
+    }
+
+    private int[] ProcessQueries(int[] queries, int upperBound, int[] thresholdForMax) {
+        return queries.Select(q => Find(q)).ToArray();
+
+        int Find(int threshold) {
+            var (left, right) = (0, upperBound);
+            while (left < right) {
+                var mid = left + (right - left + 1) / 2;
+                if (thresholdForMax[mid] < threshold) {
+                    left = mid;
+                } else {
+                    right = mid - 1;
+                }
+            }
+
+            return left;
+        }
+    }
+
+    public int[] MaxPoints(int[][] grid, int[] queries) {
+        var thresholdForMax = Dijkstra(grid);
+        return ProcessQueries(queries, grid.Length * grid[0].Length, thresholdForMax);
+    }
+}