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[Golang][Leetcode][BinaryTree]刷題系列-199-Right Side View


199. Binary Tree Right Side View


Level : Medium

原題連結 : Click

題目 :

Given the root of a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.


Example :

Note

Example 1:

Input: root = [1,2,3,null,5,null,4] Output: [1,3,4]

Example 2:

Input: root = [1,null,3] Output: [1,3]

Example 3:

Input: root = [] Output: []


解題思路 :

  • 這題是level order traversal的變化題,一樣可以用queue來解決,可以參考 leetcode102題解
  • 只需要取每個level最右邊的node

Queue解法

  • time complexity: O(n) , space complexity: O(n)

Runtime: 0 ms, faster than 100.00% of Go online submissions for Binary Tree Right Side View.


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/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func rightSideView(root *TreeNode) []int {
    
    var res []int
    
    if root == nil {
        return res
    }
    
    var queue []*TreeNode
    
    queue = append(queue, root)
    
    for len(queue) != 0 {
        
        res = append(res, queue[len(queue)-1].Val)
        
        length := len(queue)
        
        for i := 0; i < length; i++ {
            
            node := queue[0]
            
            if node.Left != nil {
                queue = append(queue, node.Left)
            }
            
            if node.Right != nil {
                queue = append(queue, node.Right)
            }
            
            queue = queue[1:]
        }
        
    }
    
    return res
    
}

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