Leetcode: convert_sorted_array_to_binary_search_tree

I. Question

Converts an sorted array into a binary search tree.

Ii. Analysis

In BST, the central traversal is a sorted-array, which is then constructed into a BST. The middle element is used as the root node. The left and right sides of this node are left and right subtree respectively. Do this recursively.

 

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

Leetcode: convert_sorted_array_to_binary_search_tree