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by Sumit Chourasia | Oct 08, 2020 | Category :coding | Tags : algorithm binary-tree data-structure easy leetcode tree

Merge Two Binary Trees - Tree - Easy - LeetCode

Merge Two Binary Trees - Tree - Easy - LeetCode

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.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    public TreeNode MergeTrees(TreeNode t1, TreeNode t2) {
        if(t1==null && t2==null){
            return null;
        }
        
        TreeNode root = new TreeNode();
        if(t1 != null){
            root.val += t1.val;
        }   
        
        if(t2 != null){
            root.val += t2.val;
        }
                
        root.left = MergeTrees(t1==null?null:t1.left,t2==null?null:t2.left);
        root.right = MergeTrees(t1==null?null:t1.right,t2==null?null:t2.right);
        return root;
    }
}

Time Complexity: O(m+n)

Space Complexity: O(m+n)

Where m and n are the nodes of tree t1 and tree t2.

Contributed By: Sumit Chourasia
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