Problem List

Merge Two Binary Trees

May 31, 2025 • Go • tree, binary tree, depth first search • easy

Problem

You are given two binary trees root1 and root2. Return the merged tree.

Approach

1. Traverse both trees simultaneously and recursively
2. Trust the base cases
3. Essentially copy over everything from root2 to root1 and if they overlap then merge

Go Solution

func mergeTrees(root1 *TreeNode, root2 *TreeNode) *TreeNode {
    if root1 == nil && root2 == nil {
        return nil
    }
    if root1 == nil {
        return root2
    }
    if root2 == nil {
        return root1
    }

    root1.Left = mergeTrees(root1.Left, root2.Left)
    root1.Val = root1.Val + root2.Val
    root1.Right = mergeTrees(root1.Right, root2.Right)

    return root1
}

LeetCode Problem Link