LeetCode 1373.二叉搜索子树的最大键值和

/**
 * 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:
    int ans;
    struct INFO{
        int sum;
        int mx,mi;
        bool valid;
    };
    INFO dfs(TreeNode *p)
    {
        TreeNode *l=p->left;
        TreeNode *r=p->right;
        int sum,mx,mi;
        bool valid;
        if(l==nullptr&&r==nullptr)
        {
            sum=mx=mi=p->val;
            valid=true;
        }
        else if(l==nullptr)
        {
            INFO info=dfs(r);
            sum=p->val+info.sum;
            mx=info.mx;
            mi=p->val;
            valid=p->val<info.mi&&info.valid;
        }
        else if(r==nullptr)
        {
            INFO info=dfs(l);
            sum=p->val+info.sum;
            mx=p->val;
            mi=info.mi;
            valid=p->val>info.mx&&info.valid;
        }
        else
        {
            INFO il=dfs(l),ir=dfs(r);
            sum=p->val+il.sum+ir.sum;
            mx=ir.mx;
            mi=il.mi;
            valid=il.mx<p->val&&p->val<ir.mi&&il.valid&&ir.valid;
        }
        if(valid) ans=max(ans,sum);
        return (INFO){sum,mx,mi,valid};
    }
    int maxSumBST(TreeNode* root) {
    dfs(root);
    return ans;
    }
};

/**
 * 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) {}
 * };
 */
#define INF 2147483647
class Solution {
public:
    int ans;
    struct INFO{
        int sum;
        int mx,mi;
        bool valid;
    };
    INFO dfs(TreeNode *p)
    {
        if(p==nullptr) return (INFO){0,-INF,INF,true};
        INFO il=dfs(p->left),ir=dfs(p->right);
        int mx=max(p->val,ir.mx),mi=min(p->val,il.mi);
        int sum=p->val+il.sum+ir.sum;
        bool valid=
            il.mx<p->val&&
            p->val<ir.mi&&
            il.valid&&
            ir.valid;
        if(valid) ans=max(ans,sum);
        return (INFO){sum,mx,mi,valid};
    }
    int maxSumBST(TreeNode* root) {
       dfs(root);
       return ans;
    }
};