[LeetCode] 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.
解题思路：
题意为构建有序数组的二分查找树。比较简单，用递归方法即可，中间的元素作为根节点，前半部分作为左孩子树，右半部分作为右孩子树。
/**
* 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* sortedArrayToBST(vector& nums) {
return sortedArrayToBSTHelper(nums, 0, nums.size()-1);
}
TreeNode* sortedArrayToBSTHelper(vector& nums, int start, int end){
if(start>end){
return NULL;
}
int middle = (start+end)/2;
TreeNode* root = new TreeNode(nums[middle]);
root->left = sortedArrayToBSTHelper(nums, start, middle - 1);
root->right = sortedArrayToBSTHelper(nums, middle + 1, end);
return root;
}
};
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