[LeetCode C++实现]1382. Balance a Binary Search Tree

看了一眼提示，首先将二叉搜索树有序保存到vector中，然后再从vector中恢复为平衡搜索二叉树。

/**
 * 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:
    TreeNode* balanceBST(TreeNode* root) {
        vector<int> nums;
        generate_vector(root,nums);
        
        return generate_BST(nums,0,nums.size() - 1);
    }
private:
    TreeNode* generate_BST(const vector<int> &nums,int start,int end) {
        if(start > end) return nullptr;
        int mid = (start + end) / 2;
        TreeNode* root = new TreeNode(nums[mid]);
        root->left = generate_BST(nums,start,mid - 1);
        root->right = generate_BST(nums,mid + 1,end);
        
        return root;
    }
    void generate_vector(TreeNode* root,vector<int> &nums) {
        if(root == nullptr) return;
        generate_vector(root->left,nums);
        nums.push_back(root->val);
        generate_vector(root->right,nums);
    }
};

运行性能:

Runtime: 136 ms, faster than 73.84% of C++ online submissions for Balance a Binary Search Tree.
Memory Usage: 63.1 MB, less than 62.05% of C++ online submissions for Balance a Binary Search Tree.

52coder

[LeetCode C++实现]1382. Balance a Binary Search Tree