题目二叉树的前序遍历 点击跳转文章目录题目描述二叉树前序遍历题目描述二叉树classTreeNode{intval;TreeNodeleft;TreeNoderight;}每个节点都有left 左孩子 right 右孩子前序遍历根 - 左 - 右/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val val; * this.left left; * this.right right; * } * } */classSolution{ListIntegerresnewArrayList();publicListIntegerpreorderTraversal(TreeNoderoot){dfs(root);returnres;}publicvoiddfs(TreeNodenode){if(nodenull){return;}res.add(node.val);//根dfs(node.left);//左dfs(node.right);//右}}