3. Pacific Atlantic Water Flow

Author: Sunjae95

pacific-atlantic-water-flow/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * bfs + memoization
+ *
+ * n = length of height
+ * m = length of height[i]
+ * time complexity: O(n*m * 4^n*m)
+ * space complexity: O(n*m)
+ */
+var pacificAtlantic = function (heights) {
+  const visited = Array.from({ length: heights.length }, (_, i) =>
+    Array.from({ length: heights[i].length }, () => false)
+  );
+  const memo = new Map();
+
+  const bfs = (row, column) => {
+    const dr = [0, 0, -1, 1];
+    const dc = [1, -1, 0, 0];
+    const queue = [[row, column]];
+    let [pacific, atlantic] = [false, false];
+    let queueIndex = 0;
+
+    while (queueIndex !== queue.length) {
+      const currentLastLength = queue.length;
+
+      while (queueIndex !== currentLastLength) {
+        const [r, c] = queue[queueIndex++];
+        visited[r][c] = `${row},${column}`;
+
+        if (memo.has(`${r},${c}`)) {
+          memo.set(`${row},${column}`, [row, column]);
+          return;
+        }
+
+        for (let i = 0; i < 4; i++) {
+          const nextR = r + dr[i];
+          const nextC = c + dc[i];
+          const isPacific = nextR === -1 || nextC === -1;
+          const isAtlantic =
+            nextR === heights.length || nextC === heights[0].length;
+
+          if (isPacific) {
+            pacific = true;
+            continue;
+          }
+          if (isAtlantic) {
+            atlantic = true;
+            continue;
+          }
+
+          if (visited[nextR][nextC] === `${row},${column}`) continue;
+
+          if (heights[r][c] < heights[nextR][nextC]) continue;
+
+          queue.push([nextR, nextC]);
+        }
+      }
+
+      if (pacific && atlantic) {
+        memo.set(`${row},${column}`, [row, column]);
+        return;
+      }
+    }
+  };
+
+  for (let row = 0; row < heights.length; row++) {
+    for (let column = 0; column < heights[row].length; column++) {
+      bfs(row, column);
+    }
+  }
+
+  return [...memo.values()];
+};