Convert Sorted Array to Binary Search Tree

Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

这道题本质上是二分搜索+递归建立二叉树

/**
 * 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 *create(vector<int> &num,int begin,int end)
    {
        if(begin>end) return NULL;
        int mid;
        mid=(end+begin)/2;
        
        TreeNode *leftNode=create(num,begin,mid-1);
        TreeNode *rightNode=create(num,mid+1,end);
        
        TreeNode *node = new TreeNode(num[mid]);
        
        node->left=leftNode;
        node->right=rightNode;
        
        return node;
    }
    
    TreeNode *sortedArrayToBST(vector<int> &num) {
        return create(num,0,num.size()-1);
        
    }
    
};