LeetCode: Convert Sorted Array to Binary Search Tree [108]

/**
 * 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 *build(vector<int>&num, int low, int high){
        if(low>high)return NULL;
        
        int mid = (low+high)/2;
        //生成根节点
        TreeNode*root=(TreeNode*)malloc(sizeof(TreeNode));
        root->val=num[mid];
        //生成左子树
        TreeNode*left=build(num, low, mid-1);
        //生成右子树
        TreeNode*right=build(num, mid+1, high);
        //构造二叉树
        root->left=left;
        root->right=right;
        return root;
    }

    TreeNode *sortedArrayToBST(vector<int> &num) {
        int size=num.size();
        if(size==0)return NULL;
        
        return build(num, 0, size-1);
    }
};