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二叉树的迭代遍历:补充Swift实现
# Conflicts: # problems/二叉树的迭代遍历.md
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@ -390,7 +390,7 @@ func inorderTraversal(root *TreeNode) []int {
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}
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```
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javaScript
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javaScript:
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```js
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@ -454,7 +454,7 @@ var postorderTraversal = function(root, res = []) {
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};
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```
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TypeScript:
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TypeScript:
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```typescript
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// 前序遍历(迭代法)
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@ -509,77 +509,63 @@ function postorderTraversal(root: TreeNode | null): number[] {
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};
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```
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Swift:
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Swift:
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> 迭代法前序遍历
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```swift
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// 前序遍历迭代法
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func preorderTraversal(_ root: TreeNode?) -> [Int] {
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var res = [Int]()
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if root == nil {
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return res
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}
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var stack = [TreeNode]()
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stack.append(root!)
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var result = [Int]()
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guard let root = root else { return result }
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var stack = [root]
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while !stack.isEmpty {
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let node = stack.popLast()!
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res.append(node.val)
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if node.right != nil {
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stack.append(node.right!)
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let current = stack.removeLast()
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// 先右后左,这样出栈的时候才是左右顺序
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if let node = current.right { // 右
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stack.append(node)
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}
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if node.left != nil {
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stack.append(node.left!)
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if let node = current.left { // 左
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stack.append(node)
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}
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result.append(current.val) // 中
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}
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return res
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return result
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}
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```
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> 迭代法中序遍历
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```swift
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func inorderTraversal(_ root: TreeNode?) -> [Int] {
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var res = [Int]()
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if root == nil {
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return res
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}
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var stack = [TreeNode]()
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var cur: TreeNode? = root
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while cur != nil || !stack.isEmpty {
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if cur != nil {
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stack.append(cur!)
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cur = cur!.left
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} else {
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cur = stack.popLast()
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res.append(cur!.val)
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cur = cur!.right
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}
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}
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return res
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}
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```
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> 迭代法后序遍历
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```swift
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// 后序遍历迭代法
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func postorderTraversal(_ root: TreeNode?) -> [Int] {
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var res = [Int]()
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if root == nil {
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return res
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}
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var stack = [TreeNode]()
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stack.append(root!)
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// res 存储 中 -> 右 -> 左
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var result = [Int]()
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guard let root = root else { return result }
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var stack = [root]
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while !stack.isEmpty {
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let node = stack.popLast()!
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res.append(node.val)
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if node.left != nil {
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stack.append(node.left!)
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let current = stack.removeLast()
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// 与前序相反,即中右左,最后结果还需反转才是后序
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if let node = current.left { // 左
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stack.append(node)
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}
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if node.right != nil {
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stack.append(node.right!)
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if let node = current.right { // 右
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stack.append(node)
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}
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result.append(current.val) // 中
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}
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return result.reversed()
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}
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// 中序遍历迭代法
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func inorderTraversal(_ root: TreeNode?) -> [Int] {
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var result = [Int]()
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var stack = [TreeNode]()
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var current: TreeNode! = root
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while current != nil || !stack.isEmpty {
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if current != nil { // 先访问到最左叶子
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stack.append(current)
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current = current.left // 左
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} else {
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current = stack.removeLast()
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result.append(current.val) // 中
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current = current.right // 右
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}
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}
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// res 翻转
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res.reverse()
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return res
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return result
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}
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```
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