【Binary tree】Right view of binary tree

0x00 topic

Given the root node of a binary tree, root
imagine yourself standing on it, 右侧
in order from 顶part to 底part
Return the value of the node that can be seen from the right

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0x01 Ideas

Equivalent to each layer, only 最右边the can be traversed
by using the method to obtain all the nodes of the current layer and save the last node层序

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0x02 solution

language:Swift

tree node:TreeNode

public class TreeNode {
    public var val: Int
    public var left: TreeNode?
    public var right: TreeNode?
    public init() { self.val = 0; self.left = nil; self.right = nil; }
    public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
    public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
        self.val = val
        self.left = left
        self.right = right
    }
}

solution:

func rightSideView(_ root: TreeNode?) -> [Int] {
    guard let r = root else { return [] }
    
    // 保存结果 
    var res: [Int] = []
    
    // 存储每一层的节点
    var queue: [TreeNode] = []
    queue.append(r)

    while (!queue.isEmpty) {
        // 获取最后一个，保存
        let node = queue.last!
        res.append(node.val)

		// 获取下一层的所有节点
        var tmp: [TreeNode] = []
        for n in queue {
            if let left = n.left {
                tmp.append(left)
            }
            if let right = n.right {
                tmp.append(right)
            }
        }
        
        // 切换到下一层
        queue = tmp
    }
    
	// 返回结果  
    return res
}

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applet application

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