[sonjh1217] WEEK 14 Solutions

counting-bits/sonjh1217.swift

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+class Solution {
+    // Brute Force
+    // O(nlogn) time / O(n) space
+    func countBits(_ n: Int) -> [Int] {
+        var numberOfOnes = [Int]()
+        for i in 0...n {
+            var numberOfOne = 0
+            var i = i
+
+            while i > 0 {
+                numberOfOne += i & 1
+                i >>= 1
+            }
+
+            numberOfOnes.append(numberOfOne)
+        }
+
+        return numberOfOnes
+    }
+
+    // Dynamic Programming
+    // O(n) time / O(n) space
+    func countBitsDP(_ n: Int) -> [Int] {
+        var numberOfOnes = [Int](repeating: 0, count: n + 1)
+        if n < 1 {
+            return numberOfOnes
+        }
+
+        for i in 1...n {
+            numberOfOnes[i] = numberOfOnes[i >> 1] + (i & 1)
+        }
+        return numberOfOnes
+
+    }
+}

subtree-of-another-tree/sonjh1217.swift

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+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public var val: Int
+ *     public var left: TreeNode?
+ *     public var right: TreeNode?
+ *     public init() { self.val = 0; self.left = nil; self.right = nil; }
+ *     public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
+ *     public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
+ *         self.val = val
+ *         self.left = left
+ *         self.right = right
+ *     }
+ * }
+ */
+class Solution {
+    // O(n * m) time / O(n) space
+    func isSubtree(_ root: TreeNode?, _ subRoot: TreeNode?) -> Bool {
+        let subRootNode = subRoot?.val
+
+        var queue = [TreeNode]()
+        guard let root = root else {
+            return false
+        }
+        queue.append(root)
+        var head = 0
+        while queue.count > head {
+            let currentNode = queue[head]
+            head += 1
+            if currentNode.val == subRootNode {
+                if dfs(node: currentNode, subRoot: subRoot) {
+                    return true
+                }
+            }
+
+            if let left = currentNode.left {
+                queue.append(left)
+            }
+            if let right = currentNode.right {
+                queue.append(right)
+            }
+        }
+
+        return false
+    }
+
+    func dfs(node: TreeNode?, subRoot: TreeNode?) -> Bool {
+        guard let node = node, let subRoot = subRoot else {
+            return node == nil && subRoot == nil
+        }
+
+        return node.val == subRoot.val
+        && dfs(node: node.left, subRoot: subRoot.left)
+        && dfs(node: node.right, subRoot: subRoot.right)
+    }
+
+}