BFS 추가

Author: sonjh1217

pacific-atlantic-water-flow/sonjh1217.swift

@@ -1,6 +1,71 @@
 class Solution {
     // O(m*n) time / O(m*n) space
-    func pacificAtlantic(_ heights: [[Int]]) -> [[Int]] {
+    func pacificAtlanticBFS(_ 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 bfs(queue: [(Int, Int)], goes: inout [[Bool]]) {
+            var queue = queue
+            var head = 0
+            for (i, j) in queue {
+                goes[i][j] = true
+            }
+            
+            while head < queue.count {
+                var (i, j) = queue[head]
+                head += 1
+                
+                for (di, dj) in directions {
+                    let ni = i + di
+                    let nj = j + dj
+                    if ni >= 0
+                        && ni < m
+                        && nj >= 0
+                        && nj < n
+                        && !goes[ni][nj]
+                        && heights[ni][nj] >= heights[i][j]  {
+                        goes[ni][nj] = true
+                        queue.append((ni, nj))
+                    }
+                }
+            }
+        }
+        
+        var pacificStarts = [(Int, Int)]()
+        var atlanticStarts = [(Int, Int)]()
+        for i in 0..<m {
+            pacificStarts.append((i, 0))
+            atlanticStarts.append((i, n-1))
+        }
+        
+        for j in 0..<n {
+            pacificStarts.append((0, j))
+            atlanticStarts.append((m-1, j))
+        }
+        
+        bfs(queue: pacificStarts, goes: &goesPacific)
+        bfs(queue: atlanticStarts, 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
+    }
+    
+    // O(m*n) time / O(m*n) space
+    func pacificAtlanticDFS(_ heights: [[Int]]) -> [[Int]] {
         var result = [[Int]]()
         guard let first = heights.first else {
             return result