diff --git a/problems/二叉树的迭代遍历.md b/problems/二叉树的迭代遍历.md index ba38726b..8164724b 100644 --- a/problems/二叉树的迭代遍历.md +++ b/problems/二叉树的迭代遍历.md @@ -390,7 +390,7 @@ func inorderTraversal(root *TreeNode) []int { } ``` -javaScript +javaScript: ```js @@ -454,7 +454,7 @@ var postorderTraversal = function(root, res = []) { }; ``` -TypeScript: +TypeScript: ```typescript // 前序遍历(迭代法) @@ -509,77 +509,63 @@ function postorderTraversal(root: TreeNode | null): number[] { }; ``` -Swift: +Swift: -> 迭代法前序遍历 ```swift +// 前序遍历迭代法 func preorderTraversal(_ root: TreeNode?) -> [Int] { - var res = [Int]() - if root == nil { - return res - } - var stack = [TreeNode]() - stack.append(root!) + var result = [Int]() + guard let root = root else { return result } + var stack = [root] while !stack.isEmpty { - let node = stack.popLast()! - res.append(node.val) - if node.right != nil { - stack.append(node.right!) + let current = stack.removeLast() + // 先右后左,这样出栈的时候才是左右顺序 + if let node = current.right { // 右 + stack.append(node) } - if node.left != nil { - stack.append(node.left!) + if let node = current.left { // 左 + stack.append(node) } + result.append(current.val) // 中 } - return res + return result } -``` -> 迭代法中序遍历 -```swift -func inorderTraversal(_ root: TreeNode?) -> [Int] { - var res = [Int]() - if root == nil { - return res - } - var stack = [TreeNode]() - var cur: TreeNode? = root - while cur != nil || !stack.isEmpty { - if cur != nil { - stack.append(cur!) - cur = cur!.left - } else { - cur = stack.popLast() - res.append(cur!.val) - cur = cur!.right - } - } - return res -} -``` - -> 迭代法后序遍历 -```swift +// 后序遍历迭代法 func postorderTraversal(_ root: TreeNode?) -> [Int] { - var res = [Int]() - if root == nil { - return res - } - var stack = [TreeNode]() - stack.append(root!) - // res 存储 中 -> 右 -> 左 + var result = [Int]() + guard let root = root else { return result } + var stack = [root] while !stack.isEmpty { - let node = stack.popLast()! - res.append(node.val) - if node.left != nil { - stack.append(node.left!) + let current = stack.removeLast() + // 与前序相反,即中右左,最后结果还需反转才是后序 + if let node = current.left { // 左 + stack.append(node) } - if node.right != nil { - stack.append(node.right!) + if let node = current.right { // 右 + stack.append(node) + } + result.append(current.val) // 中 + } + return result.reversed() +} + +// 中序遍历迭代法 +func inorderTraversal(_ root: TreeNode?) -> [Int] { + var result = [Int]() + var stack = [TreeNode]() + var current: TreeNode! = root + while current != nil || !stack.isEmpty { + if current != nil { // 先访问到最左叶子 + stack.append(current) + current = current.left // 左 + } else { + current = stack.removeLast() + result.append(current.val) // 中 + current = current.right // 右 } } - // res 翻转 - res.reverse() - return res + return result } ```