zhangdizhangdi

94.二叉树的中序遍历

题目

LeetCode 简单

题目

给定一个二叉树的根节点 root ，返回 它的 中序 遍历 。

示例：
输入：root = [1,null,2,3]
输出：[1,3,2]

题解

方法：递归

递归 O(n) O(n)

ts
function inorderTraversal(root: TreeNode | null): number[] {
  let res = []
  if (root) {
    const inorder = (node: TreeNode) => {
      if (node.left) inorder(node.left)
      res.push(node.val)
      if (node.right) inorder(node.right)
    }
    inorder(root)
  }
  return res
}

const tree = new Tree([3, 9, 20, null, null, 15, 7, 14, 13])
console.log('🌰', tree)
console.log('🌰', inorderTraversal(tree.root))

方法：迭代

栈 O(n) O(n)

ts
function inorderTraversalUseStack(root: TreeNode | null): number[] {
  let res = []
  let stack = []
  let p = root
  while (stack.length || p) {
    while (p) {
      stack.push(p)
      p = p.left
    }

    console.log('stack', JSON.stringify(stack.map(i => i.val)))

    const node = stack.pop()
    res.push(node.val)
    p = node.right
  }
  return res
}

const tree = new Tree([3, 9, 20, null, null, 15, 7, 14, 13])
console.log('🌰', tree)
console.log('🌰', inorderTraversalUseStack(tree.root))