C# 代码

public class Solution {
    public IList<int> GetAllElements(TreeNode root1, TreeNode root2) {
        List<int> list1 = new List<int>();
        List<int> list2 = new List<int>();
        InOrder(root1, list1);
        InOrder(root2, list2);
        int n = list1.Count, m = list2.Count;
        List<int> result = new List<int>();

        int i = 0, j = 0;
        while (i < n && j < m){
            if (list1[i] < list2[j]){
                result.Add(list1[i++]);
            }
            else{
                result.Add(list2[j++]);
            }
        }

        while (i < n) result.Add(list1[i++]);
        while (j < m) result.Add(list2[j++]);

        return result;
    }

    private void InOrder(TreeNode root, List<int> list){
        if (root != null){
            InOrder(root.left, list);
            list.Add(root.val);
            InOrder(root.right, list);
        }
    }
}