286. Walls and Gates

Author: partho-maple

README.md

@@ -607,6 +607,7 @@ BFS, DFS, Dijkstra, Floyd–Warshall, Bellman-Ford, Kruskal, Prim's, Minimum Spa
 |46| [364_Nested_List_Weight_Sum_II](https://tinyurl.com/w5d2ff4) | [Python](https://tinyurl.com/wu6rdaw/364_Nested_List_Weight_Sum_II.py), [Swift](https://tinyurl.com/wuja3c4/364_Nested_List_Weight_Sum_II.swift) | --- | Medium |📌 Hidden DFS |
 |47| [1245. Tree Diameter](https://tinyurl.com/yxq4uykv) | [Python](https://tinyurl.com/wu6rdaw/1245_Tree_Diameter.py), [Swift](https://tinyurl.com/wuja3c4/1245_Tree_Diameter.swift) | [Art 1](https://www.geeksforgeeks.org/longest-path-undirected-tree/) | Medium |📌 Learned, 2 BFS. Important and interesting |
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+|49| [286. Walls and Gates](https://tinyurl.com/y3ollzsl) | [Python](https://tinyurl.com/wu6rdaw/286_Walls_and_Gates.py), [Swift](https://tinyurl.com/wuja3c4/286_Walls_and_Gates.swift) | --- | Medium |📌 BFS, DFS |
 
 
 </p>
@@ -1135,6 +1136,8 @@ Check this **[Golden](https://tinyurl.com/uboo399)** posts first.
 15. [Amazon ও Google এ চাকরির সুযোগ পাওয়ার প্রস্তুতি পর্ব](https://tinyurl.com/t7dnzs8)
 16. [Coding Interviews](https://tinyurl.com/rofaykt)
 17. **[Tech Interview Handbook](https://tinyurl.com/rofaykt)**
+18. [Complete Introduction to the 30 Most Essential Data Structures & Algorithms](https://tinyurl.com/y6e8klgj)
+19. [How to Solve Any Code Challenge or Algorithm](https://tinyurl.com/y3staja5)
 
 </p>
 </details>

leetcode.com/swift/DS_ALGO_PRAC.playground/Sources/swift/286_Walls_and_Gates.swift

@@ -0,0 +1,62 @@
+// DFS
+import Foundation
+class Solution {
+    func wallsAndGates(_ rooms: inout [[Int]]) {
+        
+        var visited = Set<String>()
+        for i in 0..<rooms.count {
+            for j in 0..<rooms[0].count {
+                if rooms[i][j] == 0 {
+                    wallsAndGatesDFSHelper(&rooms, &visited, (i, j))
+                }
+            }
+        }
+    }
+    
+    func wallsAndGatesDFSHelper(_ rooms: inout [[Int]], _ visited: inout Set<String>, _ startCoord: (Int, Int)) {
+        for neighbor in [ (-1,0), (0,1), (1,0), (0,-1) ] {
+            let (newX, newY) = (startCoord.0 + neighbor.0, startCoord.1 + neighbor.1)
+            if newX >= 0 && newX < rooms.count && newY >= 0 && newY < rooms[0].count && rooms[newX][newY] != -1 && rooms[newX][newY] != 0 && !visited.contains("\(newX)-\(newY)") {
+                if rooms[newX][newY] > rooms[startCoord.0][startCoord.1] {
+                    rooms[newX][newY] = rooms[startCoord.0][startCoord.1] + 1
+                    visited.insert("\(newX)-\(newY)")
+                    wallsAndGatesDFSHelper(&rooms, &visited, (newX, newY))
+                    visited.remove("\(newX)-\(newY)")
+                }
+            }
+        }
+    }
+}
+
+// BFS
+import Foundation
+class Solution {
+    func wallsAndGates(_ rooms: inout [[Int]]) {
+        
+        var queue = [(Int, Int, Int)]()
+        var visited = Set<String>()
+        for i in 0..<rooms.count {
+            for j in 0..<rooms[0].count {
+                if rooms[i][j] == 0 {
+                    queue.append((i, j, 0))
+                }
+            }
+        }
+        
+        while !queue.isEmpty {
+            var currentLevelLength = queue.count
+            for _ in 1...currentLevelLength {
+                let (x, y, val) = queue.removeFirst()
+                
+                for neighbor in [ (-1,0), (0,1), (1,0), (0,-1) ] {
+                    let (newX, newY) = (x + neighbor.0, y + neighbor.1)
+                    if newX >= 0 && newX < rooms.count && newY >= 0 && newY < rooms[0].count && rooms[newX][newY] != -1 && rooms[newX][newY] != 0 && !visited.contains("\(newX)-\(newY)") {
+                        rooms[newX][newY] = val + 1
+                        visited.insert("\(newX)-\(newY)")
+                        queue.append((newX, newY, val + 1))
+                    }
+                }
+            }
+        }
+    }
+}