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.
思路:递归前序遍历二叉树算法的变种.
规则:
(1)若t1 和 t2都非空,访问之.并创建新节点,val为t1和t2的val之和.
然后就是前序遍历那一套
(2)若t1 t2其中有一个或两个为空,则直接返回另一个.(因为若t1已经为空,则merge之后的结果就只剩t2,直接拿过来就行.画图比较好理解)
/**
* 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) {
if (t1 && t2) {
TreeNode* node = new TreeNode(t1->val + t2->val);
node->left = mergeTrees(t1->left, t2->left);
node->right = mergeTrees(t1->right, t2->right);
return node;
} else {
return t1 ? t1 : t2;
}
}
};
