1305. All Elements in Two Binary Search Trees

Given two binary search trees root1 and root2.

Return a list containing all the integers from both trees sorted in ascending order.

 

Example 1:

Input: root1 = [2,1,4], root2 = [1,0,3]
Output: [0,1,1,2,3,4]

Example 2:

Input: root1 = [0,-10,10], root2 = [5,1,7,0,2]
Output: [-10,0,0,1,2,5,7,10]

Example 3:

Input: root1 = [], root2 = [5,1,7,0,2]
Output: [0,1,2,5,7]

Example 4:

Input: root1 = [0,-10,10], root2 = []
Output: [-10,0,10]

Example 5:

Input: root1 = [1,null,8], root2 = [8,1]
Output: [1,1,8,8]

class Solution {
    public static void dfs(TreeNode root, List<Integer> list){
        if(root == null) return;
        dfs(root.left, list);
        list.add(root.val);
        dfs(root.right, list);
    }
    public List<Integer> getAllElements(TreeNode root1, TreeNode root2) {
        List<Integer> ans = new ArrayList<>();
        List<Integer> l1 = new ArrayList<>();
        List<Integer> l2 = new ArrayList<>();
        dfs(root1, l1);
        dfs(root2, l2);
        int i1 = 0, i2 = 0;
        while(i1 < l1.size() || i2 < l2.size()){
            if(i2 == l2.size() || i1 < l1.size() && l1.get(i1) <= l2.get(i2)){
                ans.add(l1.get(i1));
                i1++;
            } else {
                ans.add(l2.get(i2));
                i2++;
            }
        }
        return ans;
    }
}