Merge Two Binary Trees(leetcode)

Merge Two Binary Trees

Merge Two Binary Trees
题目

解决

题目

leetcode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:

nput:
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.

解决

对于这种二叉树的遍历，最适用的方法就是递归。

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
// 当两个节点不为nullptr时，根据规则重叠
if (t1 != NULL && t2 != NULL) {
struct TreeNode * root = new TreeNode(t1->val + t2->val);
// 使用递归来取得对应的left和right
root->left = mergeTrees(t1->left, t2->left);
root->right = mergeTrees(t1->right, t2->right);
return root;
} else if (t1 == NULL && t2 != NULL) {
return t2;
} else if (t1 != NULL && t2 == NULL) {
return t1;
} else {
return NULL;
}
}
};