637. Average of Levels in Binary Tree

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637. Average of Levels in Binary Tree

题目描述

Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

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Example 1: 
Input: 
    3 
   / \ 
  9  20 
    /  \ 
   15   7 
Output: [3, 14.5, 11]
Explanation:
The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].

Note:
The range of node’s value is in the range of 32-bit signed integer.

题目大意

计算每层的平均数

解题思路

层次遍历

代码

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func averageOfLevels(_ root: TreeNode?) -> [Double] {
        guard let tree = root else { return [] }
        var ans = [Double]()
        var queue = [tree]
        while !queue.isEmpty {
            var sum = 0
            var tmp = [TreeNode]()
            for tree in queue {
                sum += tree.val
                if let left = tree.left { tmp.append(left) }
                if let right = tree.right { tmp.append(right) }
            }
            ans.append(Double(sum) / Double(queue.count))
            queue = tmp
        }
        return ans
    }
}
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