[LeetCode] Convert Sorted List to Binary Search Tree

[Problem]
Given a singly linked list where elements are sorted in ascendingorder, convert it to a height balanced BST.

[Analysis]
和 Convert Sorted Array to Binary Search Tree差不多，将链表中的数值用一个vector存就转换成上一题了。

[Solution]

//
// Definition for singly-linked list.
// struct ListNode {
//     int val;
//     ListNode *next;
//     ListNode(int x) : val(x), next(NULL) {}
// };
//
//
// Definition for binary tree
// struct TreeNode {
//     int val;
//     TreeNode *left;
//     TreeNode *right;
//     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
// };
//
class Solution {
public:
    // build tree
    TreeNode *build(vector &num, int begin, int end){
        if(begin > end){
            return NULL;
        }
   
        // build left brunch and right brunch
        int mid = (begin+end)/2;
        TreeNode* left = build(num, begin, mid-1);
        TreeNode* right = build(num, mid+1, end);
   
        // build tree
        TreeNode* node = new TreeNode(num[mid]);
        node->left = left;
        node->right = right;
        return node;
    }
   
    // sorted array to BST
    TreeNode *sortedArrayToBST(vector &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(num.size() == 0){
            return NULL;
        }
        else{
            return build(num, 0, num.size()-1);
        }
    }
   
    // sorted list to BST
    TreeNode *sortedListToBST(ListNode *head) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector array;
        while(head != NULL){
            array.push_back(head->val);
            head = head->next;
        }
        return sortedArrayToBST(array);
    }
};

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