feat: 200. Number of Islands

Author: gwbaik9717

number-of-islands/gwbaik9717.js

@@ -0,0 +1,71 @@
+// w: width of grid, h: height of grid
+// Time complexity: O(h*w)
+// Space complexity: O(h*w)
+
+class MyQueue {
+  constructor() {
+    this.q = [];
+    this.front = 0;
+    this.rear = 0;
+  }
+
+  get isEmpty() {
+    return this.front === this.rear;
+  }
+
+  push(value) {
+    this.q.push(value);
+    this.rear++;
+  }
+
+  pop() {
+    const value = this.q[this.front];
+    delete this.q[this.front++];
+    return value;
+  }
+}
+
+/**
+ * @param {character[][]} grid
+ * @return {number}
+ */
+var numIslands = function (grid) {
+  const h = grid.length;
+  const w = grid[0].length;
+
+  const dy = [1, 0, -1, 0];
+  const dx = [0, 1, 0, -1];
+
+  const bfs = (start) => {
+    const q = new MyQueue();
+    q.push(start);
+    const [sy, sx] = start;
+    grid[sy][sx] = "0";
+
+    while (!q.isEmpty) {
+      const [cy, cx] = q.pop();
+
+      for (let i = 0; i < dy.length; i++) {
+        const ny = cy + dy[i];
+        const nx = cx + dx[i];
+
+        if (ny >= 0 && ny < h && nx >= 0 && nx < w && grid[ny][nx] === "1") {
+          q.push([ny, nx]);
+          grid[ny][nx] = "0";
+        }
+      }
+    }
+  };
+
+  let answer = 0;
+  for (let i = 0; i < h; i++) {
+    for (let j = 0; j < w; j++) {
+      if (grid[i][j] === "1") {
+        answer++;
+        bfs([i, j]);
+      }
+    }
+  }
+
+  return answer;
+};