199. 二叉树的右视图

199. 二叉树的右视图

1广度优先遍历二叉树，右边所能看到的肯定是当前层的最后一个节点，所以这个就是求每层的最后一个节点数
2 处理好出队和入队的先后关系， 出队是把当前队列的数据都出了。但是在出队之前得把下一层数据都入队了。

package main
import "fmt"
type TreeNode struct {
    Val   int
    Left  *TreeNode
    Right *TreeNode
}
func rightSideView(root *TreeNode) []int {
    if root == nil {
        return nil
    }
    queue := make([]*TreeNode, 0)
    queue = append(queue, root)
    var res []int
    for len(queue) > 0 {
        l := len(queue)
        node := queue[l-1]
        res = append(res, node.Val)
        for i := range queue {
            currNode := queue[i]
            if currNode.Left != nil {
                queue = append(queue, currNode.Left)
            }
            if currNode.Right != nil {
                queue = append(queue, currNode.Right)
            }
        }
        queue = queue[l:]
    }
    return res
}
func main() {
    one := &TreeNode{Val: 1}
    two := &TreeNode{Val: 2}
    one.Left = two
    three := &TreeNode{Val: 3}
    one.Right = three
    //five :=&TreeNode{Val: 5}
    //two.Right = five
    four := &TreeNode{Val: 4}
    two.Left = four
    fmt.Println(rightSideView(one))
    //fmt.Println(rightSideView(one))
}