109.有序链表转换二叉搜索树.cpp

/*
 * @lc app=leetcode.cn id=109 lang=cpp
 *
 * [109] 有序链表转换二叉搜索树
 */
struct ListNode {
    int val;
    ListNode *next;
    ListNode() : val(0), next(nullptr) {}
    ListNode(int x) : val(x), next(nullptr) {}
    ListNode(int x, ListNode *next) : val(x), next(next) {}
};
struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode() : val(0), left(nullptr), right(nullptr) {}
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
};
// @lc code=start
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    // 69 24;
    // 被平衡树吓到了，其实不复杂
    TreeNode* sortedListToBST(ListNode* head) {
        vector<int> v;
        ListNode* p = head;
        while(p){
            v.push_back(p->val);
            p = p->next;
        }
        return recur(v, 0, v.size()-1);
    }

    TreeNode* recur(vector<int>& v, int begin, int end){
        if(begin > end){
            return nullptr;
        }
        int mid = (end + begin) / 2;
        TreeNode *root = new TreeNode(v[mid]);
        root->left = recur(v, begin, mid-1);
        root->right = recur(v, mid+1, end);
        return root;
    }
};
// @lc code=end