【LeetCode】144. 二叉树的前序遍历

题目https://leetcode.cn/problems/binary-tree-preorder-traversal/description/思路根放入左都放入右都放入codeclassSolution{ListIntegerlistnewArrayList();publicListIntegerpreorderTraversal(TreeNoderoot){ListIntegerlistnewArrayList();if(rootnull)returnlist;//根放入list.add(root.val);ListIntegerleftTreepreorderTraversal(root.left);list.addAll(leftTree);//左都放入ListIntegerrightTreepreorderTraversal(root.right);list.addAll(rightTree);//右都放入returnlist;}}