【leetcode】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.

 

每次把中间元素当成根节点，递归即可

 

/**
 * 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 *sortedArrayToBST(vector<int> &num) {
       
        TreeNode *root=buildTree(num,0,num.size()-1);
        return root;
    }
   
   
    TreeNode *buildTree(vector<int> &num,int l,int r)
    {
        if(l>r) return NULL;
       
        int mid=(l+r)/2;
       
        TreeNode *root=new TreeNode(num[mid]);
        root->left=buildTree(num,l,mid-1);
        root->right=buildTree(num,mid+1,r);
       
        return root;
    }
};