617. Merge Two Binary Trees

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problem

solution

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
        if(!root1 && !root2) return nullptr;
        if(!root1 || !root2) return root1?root1:root2;
        TreeNode * root = new TreeNode(0);
        root->val +=root1->val;
        root->val +=root2->val;
        
        root->left = mergeTrees(root1->left, root2->left);
        root->right = mergeTrees(root1->right, root2->right);
        return root;
        
        
    }
};

analysis

  • time complexity O(n)
  • space complexity O(n)