almaleh · June 8, 2020 00:54 · Jun 8, 2020 · Jun 8, 2020 · Jun 8, 2020
diff --git a/printXY.swift b/printXY.swift
@@ -1,4 +1,4 @@
-// Solution A: Unwind the recursion using a stack
+// Solution A: Unwind the recursion using DFS
 
 func printXY(_ n: Int) -> [String] {
 

diff --git a/printXY.swift b/printXY.swift
@@ -1,3 +1,5 @@
+// Solution A: Unwind the recursion using a stack
+
 func printXY(_ n: Int) -> [String] {
 
     var explored = Set<Int>()
@@ -38,5 +40,45 @@ func printXY(_ n: Int) -> [String] {
     return output
 }
 
+let res = printXY(4)
+res.forEach { print($0) }
+
+
+// Solution B: no stack
+
+let n = 4
+var array = [Character](repeating: "X", count: n)
+
+outerLoop: do {
+    print(String(array))
+
+    for i in 0..<n {
+        if array[i] == "X" {
+            array[i] = "Y"
+            continue outerLoop
+        }
+        array[i] = "X"
+    }
+}
+
+
+// Solution C: Recursive
+
+func printXY(_ n: Int) -> [String] {
+    guard n > 1 else {
+        return ["X", "Y"]
+    }
+
+    let next = printXY(n - 1)
+
+    var output = [String]()
+    for element in next {
+        output.append(element + "X")
+        output.append(element + "Y")
+    }
+
+    return output
+}
+
 let res = printXY(4)
 res.forEach { print($0) }
diff --git a/printXY.swift b/printXY.swift
@@ -0,0 +1,42 @@
+func printXY(_ n: Int) -> [String] {
+
+    var explored = Set<Int>()
+    var stack = [n]
+    var output = [String]()
+
+    while let last = stack.last {
+
+        let next = last - 1
+
+        if last == 1 {
+            // base case
+            output = ["X", "Y"]
+            explored.insert(last)
+
+        } else {
+
+            if explored.contains(next) {
+
+                var newOutput = [String]()
+                for element in output {
+                    newOutput.append(element + "X")
+                    newOutput.append(element + "Y")
+                }
+
+                output = newOutput
+
+            } else {
+                explored.insert(next)
+                stack.append(next)
+                continue
+            }
+        }
+
+        stack.popLast()
+    }
+
+    return output
+}
+
+let res = printXY(4)
+res.forEach { print($0) }
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