[Tree] add solutions to Binary Tree Level Order Traversal and Binary …

…Tree Level Order Traversal II

Tree/BinaryTreeLevelOrderTraversal.swift

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+/**
+ * Question Link: https://leetcode.com/problems/binary-tree-level-order-traversal/
+ * Primary idea: use a queue to help hold TreeNode, and for each level add a new Int array
+ * Time Complexity: O(n), Space Complexity: O(n)
+ * 
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public var val: Int
+ *     public var left: TreeNode?
+ *     public var right: TreeNode?
+ *     public init(_ val: Int) {
+ *         self.val = val
+ *         self.left = nil
+ *         self.right = nil
+ *     }
+ * }
+ */
+
+class BinaryTreeLevelOrderTraversal {
+    func levelOrder(root: TreeNode?) -> [[Int]] {
+        var res: [[Int]] = []
+        var queue:[TreeNode] = []
+
+        if root == nil {
+            return res
+        }
+
+        queue.append(root!)
+
+        while queue.count > 0 {
+            var size: Int = queue.count
+            var level: [Int] = []
+
+            for i in 1...size {
+                let node: TreeNode = queue[0]
+                queue.removeAtIndex(0)
+
+                level.append(node.val)
+                if let left = node.left {
+                    queue.append(left)
+                }
+                if let right = node.right {
+                    queue.append(right)
+                }
+            }
+            res.append(level)
+        }
+
+        return res
+    }
+}

Tree/BinaryTreeLevelOrderTraversalII.swift

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+/**
+ * Question Link: https://leetcode.com/problems/binary-tree-level-order-traversal-ii/
+ * Primary idea: use a queue to help hold TreeNode, and for each level add a new Int array
+ *
+ * Note: use method insertAtIndex to add each level to final result
+ *
+ * Time Complexity: O(n), Space Complexity: O(n)
+ * 
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public var val: Int
+ *     public var left: TreeNode?
+ *     public var right: TreeNode?
+ *     public init(_ val: Int) {
+ *         self.val = val
+ *         self.left = nil
+ *         self.right = nil
+ *     }
+ * }
+ */
+
+class BinaryTreeLevelOrderTraversalII {
+    func levelOrderBottom(root: TreeNode?) -> [[Int]] {
+        var res: [[Int]] = []
+        var queue: [TreeNode] = []
+
+        if root == nil {
+            return res
+        }
+
+        queue.append(root!)
+
+        while queue.count > 0 {
+            var size: Int = queue.count
+            var level: [Int] = []
+
+            for i in 1...size {
+                let node: TreeNode = queue[0]
+                queue.removeAtIndex(0)
+
+                level.append(node.val)
+                if let left = node.left {
+                    queue.append(left)
+                }
+                if let right = node.right {
+                    queue.append(right)
+                }
+            }
+            res.insert(level, atIndex:0)
+        }
+
+        return res
+    }
+}