200. Number of Islands (axross#122)

Author: Kohei Asai

Diff for: solutions/number_of_islands.ts

@@ -0,0 +1,30 @@
+// 200. Number of Islands
+// https://leetcode.com/problems/number-of-islands/
+export default function numIslands(grid: ("1" | "0")[][]): number {
+  const width = grid[0] ? grid[0].length : 0;
+  const height = grid.length;
+  let islands = 0;
+
+  function explore(y: number, x: number): void {
+    if (grid[y][x] === "0") return;
+
+    grid[y][x] = "0";
+
+    if (y - 1 >= 0) explore(y - 1, x);
+    if (y + 1 < height) explore(y + 1, x);
+    if (x - 1 >= 0) explore(y, x - 1);
+    if (x + 1 < width) explore(y, x + 1);
+  }
+
+  for (let y = 0; y < height; ++y) {
+    for (let x = 0; x < width; ++x) {
+      if (grid[y][x] === "0") continue;
+
+      islands += 1;
+
+      explore(y, x);
+    }
+  }
+
+  return islands;
+}

Diff for: solutions/number_of_islands_test.ts

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+import { test } from "https://deno.land/std/testing/mod.ts";
+import { assert } from "https://deno.land/std/testing/asserts.ts";
+import numIslands from "./number_of_islands.ts";
+
+test("200. Number of Islands", () => {
+  assert(
+    numIslands([
+      ["1", "1", "1", "1", "0"],
+      ["1", "1", "0", "1", "0"],
+      ["1", "1", "0", "0", "0"],
+      ["0", "0", "0", "0", "0"]
+    ]) === 1
+  );
+  assert(
+    numIslands([
+      ["1", "1", "0", "0", "0"],
+      ["1", "1", "0", "0", "0"],
+      ["0", "0", "1", "0", "0"],
+      ["0", "0", "0", "1", "1"]
+    ]) === 3
+  );
+});