Add Jeehay28.ts

Author: Jeehay28

pacific-atlantic-water-flow/Jeehay28.ts

@@ -0,0 +1,71 @@
+// TC: O(m * n)
+// SC: O(m * n)
+
+function pacificAtlantic(heights: number[][]): number[][] {
+  const m = heights.length;
+  const n = heights[0].length;
+
+  const pacific: boolean[][] = Array.from({ length: m }, () =>
+    Array(n).fill(false)
+  );
+  const atlantic: boolean[][] = Array.from({ length: m }, () =>
+    Array(n).fill(false)
+  );
+
+  const directions = [
+    [0, 1],
+    [0, -1],
+    [1, 0],
+    [-1, 0],
+  ];
+
+  const dfs = (row: number, col: number, visited: boolean[][]) => {
+    visited[row][col] = true;
+    // Border cells are adjacent to the ocean, so they are marked as reachable (true)
+
+    // From each ocean-border cell, we explore inward:
+    // if an adjacent cell is higher or equal, water can flow from it to the ocean
+    // → mark it as reachable (true)
+    for (const [dr, dc] of directions) {
+      const newRow = row + dr;
+      const newCol = col + dc;
+
+      if (
+        newRow >= 0 &&
+        newRow < m &&
+        newCol >= 0 &&
+        newCol < n &&
+        !visited[newRow][newCol] &&
+        heights[row][col] <= heights[newRow][newCol]
+        // heights[row][col] <= heights[newRow][newCol]
+        // → Water can flow from (newRow, newCol) to (row, col),
+        // so (row, col) is reachable from the ocean through (newRow, newCol)
+      ) {
+        dfs(newRow, newCol, visited);
+      }
+    }
+  };
+
+  for (let i = 0; i < m; i++) {
+    dfs(i, 0, pacific);
+    dfs(i, n - 1, atlantic);
+  }
+
+  for (let j = 0; j < n; j++) {
+    dfs(0, j, pacific);
+    dfs(m - 1, j, atlantic);
+  }
+
+  let result: number[][] = [];
+
+  for (let i = 0; i < m; i++) {
+    for (let j = 0; j < n; j++) {
+      if (pacific[i][j] && atlantic[i][j]) {
+        result.push([i, j]);
+      }
+    }
+  }
+
+  return result;
+}
+