Convert Sorted Array/list to Binary Search Tree

最新推荐文章于 2019-05-17 16:49:08 发布

原创最新推荐文章于 2019-05-17 16:49:08 发布 · 548 阅读

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本文介绍如何将有序数组转换为二叉搜索树，包括两种方法：一种是使用递归方法，另一种是利用中序遍历特性。通过实例演示了如何实现这两种方法，并解释了它们的工作原理。

/**
 * 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 *convert(vector<int> &num, int start, int end) {
        if (start>end) return NULL;
        int mid=start+(end-start)/2;
        TreeNode* root=new TreeNode(num[mid]);
        root->left=convert(num, start, mid-1);
        root->right=convert(num, mid+1, end);
        return root;
    }
    TreeNode *sortedArrayToBST(vector<int> &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        return convert(num, 0, num.size()-1);
    }
};

/**
 * 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:
    TreeNode *BuildTree(ListNode *&head, int start, int end) {
        if (start>end) return NULL;
        int  mid=(start+end)/2;
        TreeNode* _left=BuildTree(head, start, mid-1);
        TreeNode* root= new TreeNode(head->val);
        root->left=_left;
        head=head->next;
        root->right= BuildTree(head, mid+1, end);
        return root;
    }
    TreeNode *sortedListToBST(ListNode *head) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int num=0;
        ListNode* n=head;
        while (n!=NULL) {
            num++;
            n=n->next;
        }
        return BuildTree(head,0,num-1);
    }
};