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112 lines
1.9 KiB
Markdown
Executable File
112 lines
1.9 KiB
Markdown
Executable File
# [513. Find Bottom Left Tree Value](https://leetcode.com/problems/find-bottom-left-tree-value/)
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## 题目
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Given a binary tree, find the leftmost value in the last row of the tree.
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**Example 1**:
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Input:
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2
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/ \
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1 3
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Output:
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1
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**Example 2**:
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Input:
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1
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/ \
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2 3
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/ / \
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4 5 6
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/
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7
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Output:
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7
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**Note**: You may assume the tree (i.e., the given root node) is not **NULL**.
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## 题目大意
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给定一个二叉树，在树的最后一行找到最左边的值。注意: 您可以假设树（即给定的根节点）不为 NULL。
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## 解题思路
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- 给出一棵树，输出这棵树最下一层中最左边的节点的值。
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- 这一题用 DFS 和 BFS 均可解题。
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## 代码
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```go
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package leetcode
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/**
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* Definition for a binary tree node.
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* type TreeNode struct {
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* Val int
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* Left *TreeNode
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* Right *TreeNode
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* }
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*/
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// 解法一 DFS
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func findBottomLeftValue(root *TreeNode) int {
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if root == nil {
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return 0
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}
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res, maxHeight := 0, -1
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findBottomLeftValueDFS(root, 0, &res, &maxHeight)
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return res
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}
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func findBottomLeftValueDFS(root *TreeNode, curHeight int, res, maxHeight *int) {
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if curHeight > *maxHeight && root.Left == nil && root.Right == nil {
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*maxHeight = curHeight
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*res = root.Val
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}
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if root.Left != nil {
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findBottomLeftValueDFS(root.Left, curHeight+1, res, maxHeight)
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}
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if root.Right != nil {
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findBottomLeftValueDFS(root.Right, curHeight+1, res, maxHeight)
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}
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}
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// 解法二 BFS
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func findBottomLeftValue1(root *TreeNode) int {
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queue := []*TreeNode{root}
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for len(queue) > 0 {
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next := []*TreeNode{}
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for _, node := range queue {
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if node.Left != nil {
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next = append(next, node.Left)
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}
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if node.Right != nil {
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next = append(next, node.Right)
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}
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}
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if len(next) == 0 {
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return queue[0].Val
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}
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queue = next
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}
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return 0
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}
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``` |