LeetCode 617: Merge Two Binary Trees Solution

Master LeetCode problem 617 (Merge Two Binary Trees), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

617. Merge Two Binary Trees

Easy

Tree Depth-First Search Breadth-First Search Binary Tree

Problem Explanation

Explanation

To merge two binary trees, we need to traverse both trees simultaneously. At each step, we check if the current nodes in both trees are not null. If both nodes are not null, we update the value of the node in the first tree by adding the value of the corresponding node in the second tree. If one of the nodes is null, we take the non-null node as the merged node. If both nodes are null, the merged node will also be null. We then recursively merge the left subtree and right subtree of both trees.

Time Complexity: O(n) where n is the total number of nodes in the smaller tree Space Complexity: O(n) for the recursive call stack

Solution Code

class Solution {
    public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
        if (root1 == null) {
            return root2;
        }
        if (root2 == null) {
            return root1;
        }
        
        root1.val += root2.val;
        root1.left = mergeTrees(root1.left, root2.left);
        root1.right = mergeTrees(root1.right, root2.right);
        
        return root1;
    }
}

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