pacific atlantic water flow solution

Author: hyer0705

pacific-atlantic-water-flow/hyer0705.ts

@@ -0,0 +1,54 @@
+function pacificAtlantic(heights: number[][]): number[][] {
+  const m = heights.length;
+  const n = heights[0].length;
+
+  const directions = [
+    [0, 1],
+    [0, -1],
+    [1, 0],
+    [-1, 0],
+  ];
+
+  const helper = (row: number, col: number): boolean[][] => {
+    const canReach: boolean[][] = Array.from({ length: m }, () => Array(n).fill(false));
+
+    const queue: [number, number][] = [];
+
+    for (let i = 0; i < n; i++) {
+      canReach[row][i] = true;
+      queue.push([row, i]);
+    }
+    for (let i = 0; i < m; i++) {
+      canReach[i][col] = true;
+      queue.push([i, col]);
+    }
+
+    while (queue.length > 0) {
+      const [cx, cy] = queue.shift()!;
+
+      for (const [dx, dy] of directions) {
+        const [nx, ny] = [cx + dx, cy + dy];
+
+        if (nx >= 0 && nx < m && ny >= 0 && ny < n && !canReach[nx][ny] && heights[cx][cy] <= heights[nx][ny]) {
+          canReach[nx][ny] = true;
+          queue.push([nx, ny]);
+        }
+      }
+    }
+
+    return canReach;
+  };
+
+  const canReachPacific: boolean[][] = helper(0, 0);
+  const canReachAtlantic: boolean[][] = helper(m - 1, n - 1);
+
+  const results: number[][] = [];
+
+  for (let i = 0; i < m; i++) {
+    for (let j = 0; j < n; j++) {
+      if (canReachPacific[i][j] && canReachAtlantic[i][j]) results.push([i, j]);
+    }
+  }
+
+  return results;
+}