114. 二叉树展开为链表

这题直接递归前序遍历,然后更新每一个节点的左子节点为null,右子节点为新节点即可/** * 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; * } * } */ class Solution { public void flatten(TreeNode root) { ListTreeNode list new ArrayListTreeNode(); preorderTraversal(root, list); int size list.size(); for (int i 1; i size; i) { TreeNode prev list.get(i - 1); TreeNode curr list.get(i); prev.left null; prev.right curr; } } public void preorderTraversal(TreeNode root, ListTreeNode list) { if (root ! null) { list.add(root); preorderTraversal(root.left, list); preorderTraversal(root.right, list); } } }