104. 二叉树的最大深度

/**
 * 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
    }
    maxLen := 0
    queue := []*TreeNode{root}
    for len(queue) > 0 {
        sz := len(queue)
        for i:=0; i<sz; 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)
            }
        }
        maxLen++
    }
    return maxLen
}