使用的是递归的方式,所以时间复杂度有些高,48ms
TreeNode*newTree(std::vector<int> a,int s,int t){
TreeNode*root=NULL;
if(t-s==2){
root=new TreeNode(a[s+1]);
root->left=new TreeNode(a[s]);
root->right=new TreeNode(a[s+2]);
}else if(t-s==1){
root=new TreeNode(a[s]);
root->right=new TreeNode(a[s+1]);
root->left=NULL;
}else if(s==t)
{
root=new TreeNode(a[s]);
}
if(t-s>2){
root=new TreeNode(a[(s+t)/2]);
root->left=newTree(a,s,(s+t)/2-1);
root->right=newTree(a,(s+t)/2+1,t);
}
return root;
}
TreeNode* sortedListToBST(ListNode* head) {
std::vector<int> a;
while(head!=NULL){
a.push_back(head->val);
head=head->next;
}
int c=a.size();
TreeNode*root=newTree(a,0,c-1);
return root;
}