104 maximum depth of binary tree

104. 二叉树的最大深度

go：

/**

 * Definition for a binary tree node.

 * type TreeNode struct {

 *     Val int

 *     Left *TreeNode

 *     Right *TreeNode

 * }
 */
func maxDepth(root *TreeNode) int {
    if root == nil {
        return 0
    }

    queue := []*TreeNode{root}
    depth := 0

    for len(queue) > 0 {
        levelSize := len(queue)

        for i := 0; i < levelSize; i++ {
            node := queue[0]
            queue = queue[1 :]

            if node.Left != nil {
                queue = append(queue, node.Left)
            }

            if node.Right != nil {
                queue = append(queue, node.Right)
            }
        }

        depth++
    }

    return depth
}