0617-merge-two-binary-trees.java

class Solution {

    public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
        if (root1 == null && root2 == null) return null;

        int val1 = root1 != null ? root1.val : 0;
        int val2 = root2 != null ? root2.val : 0;

        TreeNode root = new TreeNode(val1 + val2);

        // merge left side of trees if they are not null
        root.left =
            mergeTrees(
                (root1 != null && root1.left != null) ? root1.left : null,
                (root2 != null && root2.left != null) ? root2.left : null
            );

        // merge righ side of trees if they are not null
        root.right =
            mergeTrees(
                (root1 != null && root1.right != null) ? root1.right : null,
                (root2 != null && root2.right != null) ? root2.right : null
            );

        return root;
    }
}