LeetCode_POTD_9Nov.java

/*
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:

The number of nodes in the tree is in the range [2, 5000].
0 <= Node.val <= 105

*/
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int maxAncestorDiff(TreeNode root) 
    {
        return DepthFirstSearch(root,root.val,root.val);
    }
    public int DepthFirstSearch(TreeNode root,int min,int max)
    {
        if(root == null)
        {
            return max-min;
        }
        max = Math.max(max,root.val);
        min = Math.min(min,root.val);
        return Math.max(DepthFirstSearch(root.left,min,max),DepthFirstSearch(root.right,max,min));
    }
}