solve

Author: sonjh1217

pacific-atlantic-water-flow/sonjh1217.swift

@@ -0,0 +1,53 @@
+class Solution {
+    // O(m*n) time / O(m*n) space
+    func pacificAtlantic(_ heights: [[Int]]) -> [[Int]] {
+        var result = [[Int]]()
+        guard let first = heights.first else {
+            return result
+        }
+        let m = heights.count
+        let n = first.count
+        
+        var goesPacific = Array(repeating: Array(repeating: false, count: n), count: m)
+        var goesAtlantic = Array(repeating: Array(repeating: false, count: n), count: m)
+        let directions = [(1,0), (-1,0), (0,1), (0,-1)]
+        
+        func dfs(i: Int, j: Int, goes: inout [[Bool]]) {
+            if goes[i][j] {
+                return
+            }
+            goes[i][j] = true
+            
+            for (di, dj) in directions {
+                let ni = i + di
+                let nj = j + dj
+                if ni >= 0
+                    && ni < m
+                    && nj >= 0
+                    && nj < n
+                    && heights[ni][nj] >= heights[i][j]  {
+                    dfs(i: ni, j: nj, goes: &goes)
+                }
+            }
+        }
+        
+        for i in 0..<m {
+            dfs(i: i, j: 0, goes: &goesPacific)
+            dfs(i: i, j: n-1, goes: &goesAtlantic)
+        }
+        
+        for j in 0..<n {
+            dfs(i: 0, j: j, goes: &goesPacific )
+            dfs(i: m-1, j: j, goes: &goesAtlantic )
+        }
+        
+        for i in 0..<m {
+            for j in 0..<n {
+                if goesPacific[i][j] && goesAtlantic[i][j] {
+                    result.append([i, j])
+                }
+            }
+        }
+        return result
+    }
+}