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1026. Maximum Difference Between Node and Ancestor

MediumOpen on LeetCodeProblem statement

Problem Statement

1026. Maximum Difference Between Node and Ancestor

Medium

Given the root of a binary tree, find the maximum value v for which there exist different nodes a and b where v = |a.val - b.val| and a is an ancestor of b.

A node a is an ancestor of b if either: any child of a is equal to b or any child of a is an ancestor of b.

 

Example 1:

Input: root = [8,3,10,1,6,null,14,null,null,4,7,13]
Output: 7
Explanation: We have various ancestor-node differences, some of which are given below :
|8 - 3| = 5
|3 - 7| = 4
|8 - 1| = 7
|10 - 13| = 3
Among all possible differences, the maximum value of 7 is obtained by |8 - 1| = 7.

Example 2:

Input: root = [1,null,2,null,0,3]
Output: 3

 

Constraints:

C++

Source file
/**
 * 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 res = 0;
    TreeNode* recur(TreeNode* root, int minN, int maxN){
        int value = root->val;
        minN = min(minN, value);
        maxN = max(maxN, value);
        res = max(res, max(value-minN, maxN-value));
        if (root->left){
            recur(root->left, minN, maxN);
        }
        if (root->right){
            recur(root->right, minN, maxN);
        }
        return root; //returns NULL
    }
    
    int maxAncestorDiff(TreeNode* root) {
        recur(root, 100000, 0);
        return res;
    }
};