leetcode538. 把二叉搜索树转换为累加树

class Solution {

    

    public void  order(TreeNode root,List list) {
        if (root == null) return ;

        order(root.left,list);
        list.add(root.val);
        order(root.right,list);
    }

    public int getSum(List list,int nums) {
        int sum = 0;

        for (int i = 0; i < list.size(); i++) {
            if (list.get(i) >= nums) sum += list.get(i);
         }

        return sum;
    }

    public void getAns(TreeNode root,Listlist) {
        if (root == null) return ;

        int sum = getSum(list,root.val);
        root.val = sum;

        getAns(root.left,list);
        getAns(root.right,list);
    }

    public TreeNode convertBST(TreeNode root) {
        Listlist =  new ArrayList<>();
        order(root,list);
        getAns(root,list);

        return root;
    }
}