Feat: 200. Number of Islands

Author: HC-kang

number-of-islands/HC-kang.ts

@@ -0,0 +1,66 @@
+/**
+ * https://leetcode.com/problems/number-of-islands
+ * T.C. O(m*n)
+ * S.C. O(m*n)
+ */
+// function numIslands(grid: string[][]): number {
+//   let count = 0;
+//   let dir = [[1, 0], [0, 1], [-1, 0], [0, -1]];
+
+//   function removeIsland(r: number, c: number) {
+//     if (r < 0 || r >= grid.length) return;
+//     if (c < 0 || c >= grid[0].length) return;
+//     if (grid[r][c] === '0') return;
+
+//     grid[r][c] = '0';
+//     for (let [dr, dc] of dir) {
+//       removeIsland(r + dr, c + dc);
+//     }
+//     return 1;
+//   }
+
+//   for (let r = 0; r < grid.length; r++) {
+//     for (let c = 0; c < grid[0].length; c++) {
+//       if (grid[r][c] === '0') continue;
+//       count++;
+//       removeIsland(r, c);
+//     }
+//   }
+
+//   return count;
+// }
+
+/**
+ * T.C. O(m*n)
+ * S.C. O(m*n)
+ */
+function numIslands(grid: string[][]): number {
+  let count = 0;
+  let dir = [[1, 0], [0, 1], [-1, 0], [0, -1]];
+
+  function removeIsland(r: number, c: number) {
+    const stack = [[r, c]];
+
+    while (stack.length) {
+      const [r, c] = stack.pop()!;
+      if (r < 0 || r >= grid.length) continue;
+      if (c < 0 || c >= grid[0].length) continue;
+      if (grid[r][c] === '0') continue;
+
+      grid[r][c] = '0';
+      for (let [dr, dc] of dir) {
+        stack.push([r + dr, c + dc]);
+      }
+    }
+  }
+
+  for (let r = 0; r < grid.length; r++) {
+    for (let c = 0; c < grid[0].length; c++) {
+      if (grid[r][c] === '0') continue;
+      count++;
+      removeIsland(r, c);
+    }
+  }
+
+  return count;
+}