[LeetCode] 1026. Maximum Difference Between Bode and Ancestor

 Problem : https://leetcode.com/problems/maximum-difference-between-node-and-ancestor/

Calculate the difference of node.val and the maximum and minimum value from its child trees.

Time complexity = O(N), N = total nodes of the given tree.

/**
 * 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 postOrder(root)[2];
    }
    
    int[] postOrder(TreeNode node) {
        int mi = node.val;
        int mx = node.val;
        int diff = 0;
        
        for (TreeNode child: new TreeNode[] {node.left, node.right}) {
            if (child != null) {
                // mi, mx, diff
                int[] tmp = postOrder(child);
                
                mi = Math.min(mi, tmp[0]);
                mx = Math.max(mx, tmp[1]);
                
                diff = Math.max(diff, tmp[2]); 
                diff = Math.max(diff, Math.abs(node.val - tmp[0]));
                diff = Math.max(diff, Math.abs(node.val - tmp[1])); 
            }
        }
        
        return new int[] {mi, mx, diff};
    }
}