LeetCode 333. 最大 BST 子树

NOTE:

是在阅读 geeksforgeeks Maximum sub-tree sum in a Binary Tree such that the sub-tree is also a BST 时，发现这个问题的，这篇文章已经收录于

我的解题

是按照 geeksforgeeks Maximum sub-tree sum in a Binary Tree such that the sub-tree is also a BST 中的解法写的。

#include <bits/stdc++.h>
using namespace std;

/**
 * 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) {}
 * };
 */

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)
    {
    }
};

// Information stored in every
// node during bottom up traversal
struct Info
{

    // Max Value in the subtree
    int max_val;

    // Min value in the subtree
    int min_val;

    // If subtree is BST
    bool isBST;

    // Sum of the nodes of the sub-tree
    // rooted under the current node
    int sum_of_node;

    // Max sum of BST found till now
    int currmax;
};

class Solution
{
public:
    int largestBSTSubtree(TreeNode *root)
    {
        int maxsum = INT_MIN;
        return MaxSumBSTUtil(root, maxsum).currmax;
    }
    // Returns information about subtree such as
    // subtree with maximum sum which is also a BST
    Info MaxSumBSTUtil(TreeNode *root, int &maxsum)
    {
        // Base case
        if (root == NULL)
            return
            {   INT_MIN, INT_MAX, true, 0, 0};

        // If current node is a leaf node then
        // return from the function and store
        // information about the leaf node
        if (root->left == NULL && root->right == NULL)
        {
            maxsum = max(maxsum, 1);
            return
            {   root->val, root->val, true, 1, maxsum};
        }

        // Store information about the left subtree
        Info L = MaxSumBSTUtil(root->left, maxsum);

        // Store information about the right subtree
        Info R = MaxSumBSTUtil(root->right, maxsum);

        Info BST;

        // If the subtree rooted under the current node
        // is a BST
        if (L.isBST && R.isBST && L.max_val < root->val && R.min_val > root->val)
        {

            BST.max_val = max(root->val, max(L.max_val, R.max_val));
            BST.min_val = min(root->val, min(L.min_val, R.min_val));
            BST.sum_of_node = R.sum_of_node + 1 + L.sum_of_node;
            maxsum = max(maxsum, BST.sum_of_node);

            // Update the current maximum sum_of_node
            BST.currmax = maxsum;

            BST.isBST = true;
            return BST;
        }
        else
        {
            // If the whole tree is not a BST then
            // update the current maximum sum_of_node
            BST.isBST = false;
            BST.currmax = maxsum;
            BST.sum_of_node = R.sum_of_node + 1 + L.sum_of_node;
            return BST;
        }
    }
};

int main()
{

}
// g++ test.cpp --std=c++11 -pedantic -Wall -Wextra