513.找树左下角的值

• 先序遍历

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
var depth int
var res int
var maxDep int
func dfs(root *TreeNode) {
    if root == nil {
        return
    }
    depth++
    // Fist order
    if root.Left == nil && root.Right == nil && depth > maxDep{
        maxDep = depth
        res = root.Val
    }
    dfs(root.Left)
    dfs(root.Right)
    depth--
}
func initVar() {
    depth = 0
    res = 0
    maxDep = 0
}
func findBottomLeftValue(root *TreeNode) int {
    initVar()
    dfs(root)
    return res
}

112. 路径总和

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func hasPathSum(root *TreeNode, targetSum int) bool {
     if root == nil {
        return false
    }
    targetSum -= root.Val
    if root.Left == root.Right { // root 是叶子
        return targetSum == 0
    }
    return hasPathSum(root.Left, targetSum) || hasPathSum(root.Right, targetSum)
}

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• 分类： 算法
• 标签： 算法基础 二叉树