108. Convert Sorted Array to Binary Search Tree*
https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/
题目描述
Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
Example:
Given the sorted array: [-10,-3,0,5,9],
One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:
0
/ \
-3 9
/ /
-10 5
C++ 实现 1
前向遍历. 从数组中间取值, 可以保证构建出来的树是平衡的.
/**
* 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 {
private:
TreeNode* sortedArrayToBST(vector<int> &nums, int start, int end) {
if (start > end)
return nullptr;
int mid = start + (end - start) / 2;
TreeNode *root = new TreeNode(nums[mid]);
root->left = sortedArrayToBST(nums, start, mid - 1);
root->right = sortedArrayToBST(nums, mid + 1, end);
return root;
}
public:
TreeNode* sortedArrayToBST(vector<int>& nums) {
return sortedArrayToBST(nums, 0, nums.size() - 1);
}
};