binary-tree-preorder-traversal.go

// https://leetcode.com/problems/binary-tree-preorder-traversal

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func preorderTraversal(root *TreeNode) []int {
    result := []int{}
    stack := []*TreeNode{}
    
    for root != nil {
        if root.Right != nil {
            stack = append(stack, root.Right)
        }
        
        if root.Left != nil {
            stack = append(stack, root.Left)
        }
        
        result = append(result, root.Val)
        
        if len(stack) > 0 {
            root = stack[len(stack) - 1]
            stack = stack[:len(stack) - 1]
        } else {
            root = nil
        }
    }
    
    return result
}