[Tree] Add a solution to House Robber III

Author: soapyigu

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 246 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
+[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 247 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
 
 
 ## Array
@@ -162,8 +162,9 @@
 [Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)| [Swift](./Tree/ConstructBinaryTreeInorderPostorder.swift)| Medium| O(n)| O(n)|
 [Path Sum](https://leetcode.com/problems/path-sum/)| [Swift](./Tree/PathSum.swift)| Easy| O(n)| O(n)|
 [Path Sum II](https://leetcode.com/problems/path-sum-ii/)| [Swift](./Tree/PathSumII.swift)| Medium| O(n)| O(n)|
-[Path Sum III](https://leetcode.com/problems/path-sum-iiI/)| [Swift](./Tree/PathSumIII.swift)| Easy| O(n^2)| O(1)|
+[Path Sum III](https://leetcode.com/problems/path-sum-iii/)| [Swift](./Tree/PathSumIII.swift)| Easy| O(n^2)| O(1)|
 [Bnary Tree Paths](https://leetcode.com/problems/binary-tree-paths/)| [Swift](./Tree/BnaryTreePaths.swift)| Easy| O(n)| O(n)|
+[House Robber III](https://leetcode.com/problems/house-robber-iii/)| [Swift](./Tree/HouseRobberIII.swift)| Medium| O(n)| O(1)|
 [Unique Binary Search Trees](https://leetcode.com/problems/unique-binary-search-trees/)| [Swift](./Tree/UniqueBinarySearchTrees.swift)| Medium| O(n^2)| O(n)|
 [Recover Binary Search Tree](https://leetcode.com/problems/recover-binary-search-tree/)| [Swift](./Tree/RecoverBinarySearchTree.swift)| Hard| O(n)| O(1)|
 [Merge Two Binary Trees](https://leetcode.com/problems/merge-two-binary-trees/description/) | [Swift](./Tree/MergeTwoBinaryTrees.swift) | Easy | O(n) | O(n) |
@@ -484,7 +485,7 @@
 |	[Swift](./String/LongestSubstringMostKDistinctCharacters.swift)	|	340	|	[Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/)  ♥	|	Hard
 |	[Swift](./DP/NestedListWeightSum.swift)	|	339	|	[Nested List Weight Sum](https://leetcode.com/problems/nested-list-weight-sum/)  ♥	| Easy
 |	[Swift](./Math/CountingBits.swift)	|	338	|	[Counting Bits](https://leetcode.com/problems/counting-bits/)	|	Medium
-|		|	337	|	[House Robber III](https://leetcode.com/problems/house-robber-iii/)	|	Medium
+|	[Swift](./Tree/HouseRobberIII.swift)	|	337	|	[House Robber III](https://leetcode.com/problems/house-robber-iii/)	|	Medium
 |		|	336	|	[Palindrome Pairs](https://leetcode.com/problems/palindrome-pairs/)	|	Hard
 |		|	335	|	[Self Crossing](https://leetcode.com/problems/self-crossing/)	|	Hard
 |		|	334	|	[Increasing Triplet Subsequence](https://leetcode.com/problems/increasing-triplet-subsequence/)	|	Medium

Tree/HouseRobberIII.swift

@@ -0,0 +1,40 @@
+/**
+ * Question Link: https://leetcode.com/problems/house-robber-iii/
+ * Primary idea: Using two sums to track rob sum starting from current node or not, 
+ *				 compare and get the maximum one
+ * Time Complexity: O(n), Space Complexity: O(1)
+ *
+ * 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 HouseRobberIII {
+    func rob(_ root: TreeNode?) -> Int {
+        let (robRoot, notRobRoot) = helper(root)
+        
+        return max(robRoot, notRobRoot)
+    }
+    
+    fileprivate func helper(_ node: TreeNode?) -> (Int, Int) {
+        guard let node = node else {
+            return (0, 0)
+        }
+        
+        let (robLeft, notRobLeft) = helper(node.left)
+        let (robRight, notRobRight) = helper(node.right)
+        
+        let robNode = notRobLeft + notRobRight + node.val
+        let notRobNode = max(robLeft, notRobLeft) + max(robRight, notRobRight)
+        
+        return (robNode, notRobNode)
+    }
+}