一起過來排好隊，進來捱打

1.Leetcode tag-LinkList 109.convert sorted list to binary search tree

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
/**
 * 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* sortedListToBST(ListNode* head) {
        return RecursionListToBST(head,NULL);
    }
    TreeNode* RecursionListToBST(ListNode* head,ListNode *tail){
        // linklist is empty
        if(head==tail)
            return NULL;
        // only one node in the tree
        if(head->next==tail){
            TreeNode *root=new TreeNode(head->val);
            return root;
        }
        // search the middle node 
        // excllent code segment need memorize.
        ListNode *mid=head;
        ListNode *temp=head;
        while(temp!=tail && temp->next!=tail){
            mid=mid->next;
            temp=temp->next->next;
        }
        TreeNode *root=new TreeNode(mid->val);
        root->left=RecursionListToBST(head,mid);
        root->right=RecursionListToBST(mid->next,tail);
        return root;
    }
};

// 尋找連結串列重點這個真的是棒

 ListNode *mid=head;
 ListNode *temp=head;
 while(temp!=tail && temp->next!=tail){
         mid=mid->next;
         temp=temp->next->next;
  }