Create 0417-pacific-atlantic-water-flow.swift

Author: drxlx

swift/0417-pacific-atlantic-water-flow.swift

@@ -0,0 +1,40 @@
+class Solution {
+    func pacificAtlantic(_ heights: [[Int]]) -> [[Int]] {
+        let rows = heights.count 
+        let cols = heights[0].count
+        var pac = Set<[Int]>()
+        var atl = Set<[Int]>()
+        var res = [[Int]]()
+
+        func dfs(_ r: Int, _ c: Int, _ visit: inout Set<[Int]>, _ prevHeight: Int) {
+            if r < 0 || c < 0 || r == rows || c == cols || visit.contains([r, c]) || heights[r][c] < prevHeight {
+                return
+            }
+            visit.insert([r, c])
+            dfs(r + 1, c, &visit, heights[r][c])
+            dfs(r - 1, c, &visit, heights[r][c])
+            dfs(r, c + 1, &visit, heights[r][c])
+            dfs(r, c - 1, &visit, heights[r][c])
+        }
+
+        for c in 0..<cols {
+            dfs(0, c, &pac, heights[0][c])
+            dfs(rows - 1, c, &atl, heights[rows - 1][c])
+        }
+
+        for r in 0..<rows {
+            dfs(r, 0, &pac, heights[r][0])
+            dfs(r, cols - 1, &atl, heights[r][cols - 1])
+        }
+
+        for r in 0..<rows {
+            for c in 0..<cols {
+                if pac.contains([r, c]) && atl.contains([r, c]) {
+                    res.append([r, c])
+                }
+            }
+        }
+
+        return res
+    }
+}