TreeNode* _sortedArrayToBST(vector<int>& num, int pos, int len) {
if (len <= 0) return NULL;
int mid = pos + len / 2;
TreeNode* root = new TreeNode(num[mid]);
root -> left = _sortedArrayToBST(num, pos, mid - pos);
root -> right = _sortedArrayToBST(num, mid + 1, len - (mid - pos + 1));
return root;
}
TreeNode* _sortedArrayToBST(vector<int>& num, int start, int end){
if(start==end)
return new TreeNode(num[start]);
if(start>end) {
return NULL;
}
int mid=start+(end-start)/2;
TreeNode* root=new TreeNode(num[mid]);
root->left=_sortedArrayToBST(num, start,mid-1);
root->right=_sortedArrayToBST(num,mid+1,end);
return root;
}
TreeNode* _sortedArrayToBST(vector<int>& num, int start, int end) {
if (end < start) {
return nullptr;
}
int mid = start + (end - start) / 2;
TreeNode* subroot = new TreeNode(num[mid]);
subroot->left = _sortedArrayToBST(num, start, mid - 1);
subroot->right = _sortedArrayToBST(num, mid + 1, end);
return subroot;
}
TreeNode* sortedArrayToBST(vector<int>& nums) {
return _sortedArrayToBST(nums, 0, nums.size() - 1);
}
TreeNode *sortedArrayToBST(vector<int> &num) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
return _sortedArrayToBST(num, 0, num.size());
}
TreeNode *sortedArrayToBST(vector<int> &num) {
if (num.empty()) {
return nullptr;
}
return _sortedArrayToBST(num, 0, num.size() - 1);
}
