[LeetCode 108] Convert Sorted Array to Binary Search Tree

题目内容

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.
题目来源

题目分析

因为有序，此题不需要将数字插入二叉树时进行平衡二叉树操作。只需每次将数组中间的数字作为根，左右数组分别作为左右子树重复上述操作即可。
注意示例代码中递归方式较为简洁，值得学习。

代码示例

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