leetcode_ Add to List 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.

將一個排好的數組轉換成平衡二叉樹，就是說，每次從中間分開，左邊作爲左子樹，右邊作爲右子樹。

代碼：

/**
 * 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;
        vector<int> leftNum(nums.begin(), nums.begin()+mid);
        vector<int> rightNum(nums.begin()+mid+1, nums.end());
        
        TreeNode *root = new TreeNode(nums[mid]);
        root->left = sortedArrayToBST(leftNum);
        root->right = sortedArrayToBST(rightNum);
        
        return root;
    }
};