LeetCode题解：Convert Sorted Array to Binary Search Tree

Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

思路：

给定一个区间[left, right]，取其中值mid=(left+right)/2对应的元素作为二叉树的根。二叉树的左子树根的值为对[left, mid-1]继续操作的结果，右子树类似。

题解：

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* generateBST(int left, int right, vector<int>& num)
{
if (left > right)
return nullptr;
else if (left == right)
return new TreeNode(num[left]);
else
{
int mid = (left + right) / 2;
TreeNode* node = new TreeNode(num[mid]);
node->left = generateBST(left, mid - 1, num);
node->right = generateBST(mid + 1, right, num);
return node;
}
}

TreeNode *sortedArrayToBST(vector<int> &num) {
return generateBST(0, num.size() - 1, num);
}
};