617. Merge Two Binary Trees

Leetcode 链接

题目

Given two binary trees and 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 them 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 new tree.

Example 1:
Input: 
    Tree 1                     Tree 2                  
          1                         2                             
         / \                       / \                            
        3   2                     1   3                        
       /                           \   \                      
      5                             4   7                  
Output: 
Merged tree:
         3
        / \
       4   5
      / \   \ 
     5   4   7
Note: The merging process must start from the root nodes of both trees.

题意解析

给出两个二叉树，合并成一棵树，相同位置上的 val 进行相加求和。

解决方案

• 简单递归即可解决问题
• 要注意判断节点为空的情况：（1）两棵树当前节点都为空 （2）其中一颗树当前节点为空

Go 代码

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

func mergeTrees(t1 *TreeNode, t2 *TreeNode) *TreeNode {
    switch {
    case t1 == nil && t2 == nil:
        return nil

    case t1 == nil:
        return t2

    case t2 == nil:
        return t1
    }

    root := &TreeNode{
        Val: t1.Val + t2.Val,
    }

    root.Left = mergeTrees(t1.Left, t2.Left)
    root.Right = mergeTrees(t1.Right, t2.Right)
    return root
}