Feat: 417. Pacific Atlantic Water Flow

pacific-atlantic-water-flow/HC-kang.ts

@@ -0,0 +1,115 @@
+/**
+ * https://leetcode.com/problems/pacific-atlantic-water-flow
+ * T.C. O((m * n)^2)
+ * S.C. O(m * n)
+ */
+function pacificAtlantic(heights: number[][]): number[][] {
+  const dir = [
+    [0, 1],
+    [0, -1],
+    [1, 0],
+    [-1, 0],
+  ];
+
+  function pacificDfs(row: number, col: number, visited: Set<string>) {
+    const key = `${row},${col}`;
+    if (visited.has(key)) return;
+    visited.add(key);
+
+    if (row === 0 || col === 0) {
+      // left or top
+      return true;
+    }
+
+    for (let [r, c] of dir) {
+      if (row + r < 0 || row + r >= heights.length) continue;
+      if (col + c < 0 || col + c >= heights[0].length) continue;
+      if (heights[row][col] < heights[row + r][col + c]) continue;
+      if (pacificDfs(row + r, col + c, visited)) return true;
+    }
+    return false;
+  }
+
+  function atlanticDfs(row: number, col: number, visited: Set<string>) {
+    const key = `${row},${col}`;
+    if (visited.has(key)) return;
+    visited.add(key);
+
+    if (row === heights.length - 1 || col === heights[0].length - 1) {
+      // right or bottom
+      return true;
+    }
+
+    for (let [r, c] of dir) {
+      if (row + r < 0 || row + r >= heights.length) continue;
+      if (col + c < 0 || col + c >= heights[0].length) continue;
+      if (heights[row][col] < heights[row + r][col + c]) continue;
+      if (atlanticDfs(row + r, col + c, visited)) return true;
+    }
+    return false;
+  }
+
+  const result: number[][] = [];
+  for (let i = 0; i < heights.length; i++) {
+    for (let j = 0; j < heights[0].length; j++) {
+      if (
+        pacificDfs(i, j, new Set<string>()) &&
+        atlanticDfs(i, j, new Set<string>())
+      ) {
+        result.push([i, j]);
+      }
+    }
+  }
+
+  return result;
+}
+
+/**
+ * T.C. O(m * n)
+ * S.C. O(m * n)
+ */
+function pacificAtlantic(heights: number[][]): number[][] {
+  const pacific: Set<string> = new Set();
+  const atlantic: Set<string> = new Set();
+
+  const dir = [
+    [0, 1],
+    [0, -1],
+    [1, 0],
+    [-1, 0],
+  ];
+
+  function dfs(row: number, col: number, visited: Set<string>) {
+    const key = `${row},${col}`;
+    if (visited.has(key)) return;
+    visited.add(key);
+
+    for (let [r, c] of dir) {
+      if (row + r < 0 || row + r >= heights.length) continue;
+      if (col + c < 0 || col + c >= heights[0].length) continue;
+      if (heights[row][col] > heights[row + r][col + c]) continue;
+      dfs(row + r, col + c, visited);
+    }
+  }
+
+  for (let i = 0; i < heights.length; i++) {
+    dfs(i, 0, pacific);
+    dfs(i, heights[0].length - 1, atlantic);
+  }
+
+  for (let i = 0; i < heights[0].length; i++) {
+    dfs(0, i, pacific);
+    dfs(heights.length - 1, i, atlantic);
+  }
+
+  const result: number[][] = [];
+
+  for (const p of pacific) {
+    if (atlantic.has(p)) {
+      const [row, col] = p.split(',').map(Number);
+      result.push([row, col]);
+    }
+  }
+
+  return result;
+}