展平二叉搜索树

展平二叉搜索树

class Solution {

    //定义一个容器将中序遍历之后的节点存起来(升序)
    public List<TreeNode> list = new ArrayList<>();

    public TreeNode increasingBST(TreeNode root) {
        preTravel(root);

        TreeNode head=list.get(0);

        TreeNode temp=head;

        for (int i = 1; i < list.size(); i++) {
            //获得下一个节点
            temp.right=list.get(i);
            //将当前节点的左孩子置空
            temp.left=null;
            //将临时节点指为当前节点的右子节点
            temp=temp.right;
            //将当前节点的左孩子置空
            temp.left=null;
        }

        return head;
    }

    //中序遍历
    public void preTravel(TreeNode root){
        if(root==null){
            return;
        }

        preTravel(root.left);
        list.add(root);
        preTravel(root.right);
    }
}

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;
     }
}