102. 二叉树的层序遍历

二叉树的层序遍历

• 难度: medium
• 原始链接: https://leetcode.cn/problems/binary-tree-level-order-traversal
• 标签: 层序遍历

解法一: 广度优先遍历

go

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func levelOrder(root *TreeNode) [][]int {
  if root == nil {
    return [][]int{}
  }
  queue := []*TreeNode{root}
  var ans [][]int
  for len(queue) > 0 {
    size := len(queue)
    var list []int
    for i := 0; i < size; i++ {
      node := queue[i]
      list = append(list, node.Val)
      if node.Left != nil {
        queue = append(queue, node.Left)
      }
      if node.Right != nil {
        queue = append(queue, node.Right)
      }
    }
    queue = queue[size:]
    ans = append(ans, list)
  }
  return ans
}

解法二: 深度优先遍历

Go

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func levelOrder(root *TreeNode) [][]int {
  var ans [][]int
  var dfs func(*TreeNode, int)
  dfs = func(node *TreeNode, depth int) {
    if node == nil {
      return
    }
    if len(ans) <= depth {
      ans = append(ans, []int{})
    }
    ans[depth] = append(ans[depth], node.Val)
    dfs(node.Left, depth+1)
    dfs(node.Right, depth+1)
  }
  dfs(root, 0)
  return ans
}