LeetCode 617 Merge two Binary Tree in JavaScript

Problem Statement

You are given two binary trees root1 and root2.

Imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not. You need to merge the two trees into a new binary tree. The merge rule is that if two nodes overlap, then sum node values up as the new value of the merged node. Otherwise, the NOT null node will be used as the node of the new tree.

Return the merged tree.

Note: The merging process must start from the root nodes of both trees.

Input: root1 = [1,3,2,5], root2 = [2,1,3,null,4,null,7]
Output: [3,4,5,5,4,null,7]

Solution:

This problem can be solved using recursion easily.

If any one of the tree is null then other tree will be output.

We can traverse the both tree together and if both node is not null, we will traverse subtree.

Code is as follows

var mergeTrees = function(root1, root2) {
    if(root1==null)
        return root2;
    if(root2===null)
        return root1;
    if(root1==null && root2===null)
        return null;
    if(root1!==null && root2!==null)
        {
            root1.val+=root2.val; // find the sum of two nodes
            root1.left=mergeTrees(root1.left,root2.left);
            root1.right=mergeTrees(root1.right,root2.right);
            return root1; // return the final root of tree
        }
};