108. Convert Sorted Array to Binary Search Tree
Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
Example:
Given the sorted array: [-10,-3,0,5,9],
One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:
0
/ \
-3 9
/ /
-10 5
/**
* 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<int>& nums) {
if (nums.size() == 0) return NULL;
if (nums.size() == 1)
{
return new TreeNode(nums[0]);
}
int mid = nums.size() / 2;
TreeNode *root = new TreeNode(nums[mid]);
vector<int> leftNs(nums.begin(), nums.begin() + mid);
vector<int> rightNs(nums.begin() + mid + 1, nums.end());
root->left = sortedArrayToBST(leftNs);
root->right = sortedArrayToBST(rightNs);
return root;
}
};
法二:
/**
* 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<int>& nums) {
if (nums.size() == 0)
{
return nullptr;
}
if(nums.size() == 1)
{
return new TreeNode(nums[0]);
}
int mid = (0 + nums.size()) / 2;
TreeNode *root = new TreeNode(nums[mid]);
root->left = sortedArrayToBST(nums, 0, mid - 1);
root->right = sortedArrayToBST(nums, mid + 1, nums.size() - 1);
return root;
}
TreeNode* sortedArrayToBST(vector<int>& nums, int start, int end){
if (start > end) return nullptr;
int mid = (start + end) / 2;
TreeNode *root = new TreeNode(nums[mid]);
root->left = sortedArrayToBST(nums, start, mid - 1);
root->right = sortedArrayToBST(nums, mid + 1, end);
return root;
}
};
来源:oschina
链接:https://my.oschina.net/u/4381386/blog/3522984