题目：

题解：

func minDepth(root *TreeNode) int {
    if root == nil {
        return 0
    }
    queue := []*TreeNode{}
    count := []int{}
    queue = append(queue, root)
    count = append(count, 1)
    for i := 0; i < len(queue); i++ {
        node := queue[i]
        depth := count[i]
        if node.Left == nil && node.Right == nil {
            return depth
        }
        if node.Left != nil {
            queue = append(queue, node.Left)
            count = append(count, depth + 1)
        }
        if node.Right != nil {
            queue = append(queue, node.Right)
            count = append(count, depth + 1)
        }
    }
    return 0
}