0513. Find Bottom Left Tree Value

513. Find Bottom Left Tree Value#

题目 #

Given a binary tree, find the leftmost value in the last row of the tree.

Example 1:

``````Input:

2
/ \
1   3

Output:
1
``````

Example 2:

``````Input:

1
/ \
2   3
/   / \
4   5   6
/
7

Output:
7
``````

Note: You may assume the tree (i.e., the given root node) is not NULL.

解题思路 #

• 给出一棵树，输出这棵树最下一层中最左边的节点的值。
• 这一题用 DFS 和 BFS 均可解题。

代码 #

``````
package leetcode

/**
* Definition for a binary tree node.
* type TreeNode struct {
*     Val int
*     Left *TreeNode
*     Right *TreeNode
* }
*/

// 解法一 DFS
func findBottomLeftValue(root *TreeNode) int {
if root == nil {
return 0
}
res, maxHeight := 0, -1
findBottomLeftValueDFS(root, 0, &res, &maxHeight)
return res
}

func findBottomLeftValueDFS(root *TreeNode, curHeight int, res, maxHeight *int) {
if curHeight > *maxHeight && root.Left == nil && root.Right == nil {
*maxHeight = curHeight
*res = root.Val
}
if root.Left != nil {
findBottomLeftValueDFS(root.Left, curHeight+1, res, maxHeight)
}
if root.Right != nil {
findBottomLeftValueDFS(root.Right, curHeight+1, res, maxHeight)
}
}

// 解法二 BFS
func findBottomLeftValue1(root *TreeNode) int {
queue := []*TreeNode{root}
for len(queue) > 0 {
next := []*TreeNode{}
for _, node := range queue {
if node.Left != nil {
next = append(next, node.Left)
}
if node.Right != nil {
next = append(next, node.Right)
}
}
if len(next) == 0 {
return queue[0].Val
}
queue = next
}
return 0
}

``````

Sep 6, 2020