feat: 417. Pacific Atlantic Water Flow

Author: gwbaik9717

pacific-atlantic-water-flow/gwbaik9717.js

@@ -0,0 +1,131 @@
+// n: height, m: width
+// Time complexity: O(n*m)
+// Space complexity: O(n*m)
+
+class _Queue {
+  constructor() {
+    this.q = [];
+    this.start = 0;
+    this.end = 0;
+  }
+
+  isEmpty() {
+    return this.start === this.end;
+  }
+
+  push(value) {
+    this.q.push(value);
+    this.end++;
+  }
+
+  pop() {
+    const rv = this.q[this.start];
+    delete this.q[this.start++];
+    return rv;
+  }
+}
+/**
+ * @param {number[][]} heights
+ * @return {number[][]}
+ */
+var pacificAtlantic = function (heights) {
+  const dy = [1, 0, -1, 0];
+  const dx = [0, 1, 0, -1];
+
+  const h = heights.length;
+  const w = heights[0].length;
+  const checked = Array.from({ length: h }, () =>
+    Array.from({ length: w }, () => [false, false])
+  );
+
+  // 태평양
+  const pacific = new _Queue();
+
+  for (let i = 0; i < h; i++) {
+    if (!checked[i][0][0]) {
+      pacific.push([i, 0]);
+      checked[i][0][0] = true;
+    }
+  }
+
+  for (let i = 0; i < w; i++) {
+    if (!checked[0][i][0]) {
+      pacific.push([0, i]);
+      checked[0][i][0] = true;
+    }
+  }
+
+  while (!pacific.isEmpty()) {
+    const [cy, cx] = pacific.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 &&
+        !checked[ny][nx][0] &&
+        heights[ny][nx] >= heights[cy][cx]
+      ) {
+        checked[ny][nx][0] = true;
+        pacific.push([ny, nx]);
+      }
+    }
+  }
+
+  // 대서양
+  const answer = [];
+  const atlantic = new _Queue();
+
+  for (let i = 0; i < h; i++) {
+    if (!checked[i][w - 1][1]) {
+      atlantic.push([i, w - 1]);
+      checked[i][w - 1][1] = true;
+    }
+
+    if (checked[i][w - 1][0] === true) {
+      answer.push([i, w - 1]);
+    }
+  }
+
+  for (let i = 0; i < w; i++) {
+    if (!checked[h - 1][i][1]) {
+      atlantic.push([h - 1, i]);
+      checked[h - 1][i][1] = true;
+
+      if (checked[h - 1][i][0] === true) {
+        answer.push([h - 1, i]);
+      }
+    }
+  }
+
+  while (!atlantic.isEmpty()) {
+    const [cy, cx] = atlantic.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 &&
+        !checked[ny][nx][1] &&
+        heights[ny][nx] >= heights[cy][cx]
+      ) {
+        if (checked[ny][nx][0] === true) {
+          answer.push([ny, nx]);
+        }
+
+        checked[ny][nx][1] = true;
+        atlantic.push([ny, nx]);
+      }
+    }
+  }
+
+  return answer;
+};