Easy to understand O(N) recursive solution without extra memory


  • 0
    R
    public class Solution {
        public TreeNode MergeTrees(TreeNode t1, TreeNode t2)
        {
            if(t1 == null && t2 == null) return null;
            if(t2 == null) return t1;
            if(t1 == null) return t2;
    
            t1.val += (t1 != t2) ? t2.val : 0;
            if(t1.left == null) t1.left = t2.left;
            if(t1.right == null) t1.right = t2.right;
            MergeTrees(t1.left, t2.left);
            MergeTrees(t1.right, t2.right);
            
            return t1;
        }
    }
    

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