题目描述
Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
/**
* 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 *build(vector<int>&num,int start,int end) {
if(start>=end) {
return NULL;
}
int mid=start+(end-start)/2;
TreeNode *node=new TreeNode(num[mid]);
node->left=build(num,start,mid);
node->right=build(num,mid+1,end);
return node;
}
TreeNode *sortedArrayToBST(vector<int> &num) {
if(num.size()==0) return NULL;
return build(num,0,num.size());
}
};
class Solution {
public:
TreeNode *constructtree(vector<int> &num,int begin,int end){
if(begin>end) return nullptr;
int mid=(begin+end+1)/2;
TreeNode *root=new TreeNode(num[mid]);
if(begin<mid){
root->left=constructtree(num,begin,mid-1);
root->right=constructtree(num,mid+1,end);
}
return root;
}
TreeNode *sortedArrayToBST(vector<int> &num) {
if(num.size()==0) return nullptr;
return constructtree(num,0,num.size()-1);
}
};