[Swift]LeetCode314. 二叉樹的豎直遍歷 $ Binary Tree Vertical Order Traversal

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Given a binary tree, return the vertical order traversal of its nodes' values. (ie, from top to bottom, column by column).node

If two nodes are in the same row and column, the order should be from left to right.git

Examples:
Given binary tree [3,9,20,null,null,15,7],github

    3
   / \
  9  20
    /  \
   15   7

return its vertical order traversal as:微信

[
  [9],
  [3,15],
  [20],
  [7]
]

Given binary tree [3,9,20,4,5,2,7],app

     3
   /   \
  9    20
 / \   / \
4   5 2   7

return its vertical order traversal as:spa

[
  [4],
  [9],
  [3,5,2],
  [20],
  [7]
]

給定二叉樹,返回其節點值的垂直順序遍歷。(即自上而下逐列)。code

 

若是兩個節點在同一行和同一列中,則順序應該從左到右。htm

 

實例:blog

給定的二叉樹[3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

返回其垂直順序遍歷爲:

[
  [9],
  [3,15],
  [20],
  [7]
]

給定二叉樹

[3,9,20,4,5,2,7],

     3
   /   \
  9    20
 / \   / \
4   5 2   7

返回其垂直順序遍歷爲:

[
  [4],
  [9],
  [3,5,2],
  [20],
  [7]
]

Solution:
 1 public class TreeNode {
 2     public var val: Int
 3     public var left: TreeNode?
 4     public var right: TreeNode?
 5     public init(_ val: Int) {
 6         self.val = val
 7         self.left = nil
 8         self.right = nil
 9     }
10 }
11 
12 class Solution {
13     func verticalOrder(_ root: TreeNode?) ->[[Int]] {
14         var res:[[Int]] = [[Int]]()
15         if root == nil {return res}
16         var m:[Int:[Int]] = [Int:[Int]]()
17         var q:[(Int,TreeNode?)] = [(Int,TreeNode?)]()
18         q.append((0, root))
19         while(!q.isEmpty)
20         {
21             var a:(Int,TreeNode?) = q.first!
22             q.popLast()
23             m[a.0,default:[Int]()].append(a.1!.val)
24             if a.1?.left != nil
25             {
26                 q.append((a.0 - 1, a.1!.left))
27             }
28             if a.1?.right != nil
29             {
30                 q.append((a.0 + 1, a.1!.right))
31             }
32         }
33         for a in m
34         {
35             res.append(a.1)
36         }
37         return res             
38     }
39 }
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