leetCode # Convert Sorted List to Binary Search Tree-优快云博客

本文介绍了一种算法，该算法将已排序的链表转换为平衡的二叉搜索树。通过选取链表中间元素作为根节点，并递归地构建左右子树，实现了链表到二叉树的有效转换。

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题目：将排好序的链表转化为二叉搜索树

分析：算法思路是取中间为根节点，左边是左子树，右边是右子树，然后递归

答案：

/**
 * 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 {
private:
TreeNode* createTree(ListNode* head, int left, int right){
    if (left > right)
        return NULL;
    int mid = (left+right)/2;
    // find mid node
    ListNode* cNode = head;
    for (int i = left; i < mid; i++){
        cNode = cNode->next;
    }
    TreeNode* tNode = new TreeNode(cNode->val);
    tNode->left = createTree(head, left,mid-1);
    tNode->right = createTree(cNode->next, mid+1, right);
    return tNode;
}
int getLength(ListNode* head){
    int len = 0;
    ListNode* p = head;
    while(p){
        p = p->next;
        len++;
    }
    return len;
}
public:
    TreeNode* sortedListToBST(ListNode* head) {
        createTree(head,0,getLength(head)-1);
    }
};

注意：很有意思的一个问题是边界的判断。我一开始把最后一句写成createTree(head,0,getLength(head))就出现了无限循环