number of islands solution

Author: hyer0705

number-of-islands/hyer0705.ts

@@ -0,0 +1,52 @@
+function numIslands(grid: string[][]): number {
+  const m = grid.length;
+  const n = grid[0].length;
+
+  const LAND = "1";
+  const WATER = "0";
+
+  const visited: boolean[][] = Array.from({ length: m }, () => Array(n).fill(false));
+
+  const isValid = (row: number, col: number): boolean => row >= 0 && row < m && col >= 0 && col < n;
+
+  const bfs = (row: number, col: number): void => {
+    const directions = [
+      [0, 1],
+      [0, -1],
+      [1, 0],
+      [-1, 0],
+    ];
+
+    // [row, col][]
+    const queue: number[][] = [];
+
+    visited[row][col] = true;
+    queue.push([row, col]);
+
+    while (queue.length > 0) {
+      const [cx, cy] = queue.shift()!;
+
+      for (const [dx, dy] of directions) {
+        const [nx, ny] = [cx + dx, cy + dy];
+
+        if (isValid(nx, ny) && !visited[nx][ny] && grid[nx][ny] === LAND) {
+          visited[nx][ny] = true;
+          queue.push([nx, ny]);
+        }
+      }
+    }
+  };
+
+  let island = 0;
+
+  for (let i = 0; i < m; i++) {
+    for (let j = 0; j < n; j++) {
+      if (grid[i][j] === LAND && !visited[i][j]) {
+        island++;
+        bfs(i, j);
+      }
+    }
+  }
+
+  return island;
+}