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| import Foundation
class MyTreeNodeSolution {
//递归
func preorderTraversal(_ root: TreeNode?,_ n: inout [Int]) {
if root == nil {
return
}
n.append(root!.val)
preorderTraversal(root?.left, &n)
preorderTraversal(root?.right, &n)
}
//非递归
func preorderTraversal2(_ root: TreeNode?) -> [Int] {
var node = root
var stack = [TreeNode?]()
var res = [Int]()
while !stack.isEmpty || node != nil {
if node != nil {
res.append(node!.val)
stack.append(node)
node = node?.left
}else {
node = stack.removeLast()?.right
}
}
return res
}
}
|
算法思想：前序遍历：根结点 —> 左子树 —> 右子树
github地址：https://github.com/cubegao/LeetCode
