[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.

 

BST的规则就是左<根<右，所有这道题和二分搜索差不多。

注意处理的细节，是的无论奇数个num还是偶数个num都适用。

适用递归实现。

/**
 * 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 createTree(nums,0,nums.size()-1);
    }
    TreeNode* createTree(vector<int>& nums,int left,int right)
    {
        if(left>right) return NULL;
        int mid = (left+right)/2;
        TreeNode* leftTree = createTree(nums,left,mid-1);
        TreeNode* rightTree = createTree(nums,mid+1,right);
        TreeNode* root = new TreeNode(nums[mid]);
        root->left = leftTree;
        root->right = rightTree;
        return root;
    }
};