二叉树层序遍历-求每层平均值

使用队列存储当前层级的节点个数

fun averageOfLevels(root: TreeNode?): DoubleArray {
        var queue = LinkedList<TreeNode>()
        val sums = arrayListOf<Double>()
        if (null == root) return doubleArrayOf()
        queue.add(root)
        var size = 1
        while (queue.isNotEmpty()) {
            var tempSum = 0.0
            val tempCount = size
            var nextLCount = 0
            while (size > 0) {
                val node = queue.poll()
                tempSum += node.`val`
                if (null != node.left) {
                    queue.add(node.left)
                    nextLCount++
                }
                if (null != node.right) {
                    queue.add(node.right)
                    nextLCount++
                }
                size--
            }
            sums.add(tempSum / tempCount)
            size = nextLCount
        }
        val doubleArray = DoubleArray(sums.size)
        sums.forEachIndexed { index, d -> 
            doubleArray.set(index,d)
        }
        return doubleArray
    }