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by Sumit Chourasia | Oct 08, 2020 | Category :coding | Tags : algorithm binary-tree data-structure easy leetcode tree

Longest Univalue Path - Tree - Easy - LeetCode

Longest Univalue Path - Tree - Easy - LeetCode

Given a binary tree, find the length of the longest path where each node in the path has the same value. This path may or may not pass through the root.

The length of path between two nodes is represented by the number of edges between them.

 

Example 1:

Input:

              5
             / \
            4   5
           / \   \
          1   1   5
Output: 2

 

Example 2:

Input:

              1
             / \
            4   5
           / \   \
          4   4   5
Output: 2

 

Note: The given binary tree has not more than 10000 nodes. The height of the tree is not more than 1000.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    int max = 0;
    public int LongestUnivaluePath(TreeNode root) {
        if(root==null){
            return 0;
        }        
        
        Helper(root,null);
        return max;
    }
    
    private int Helper(TreeNode root, int? parent){
        if(root == null){
            return 0;
        }
        
        int left = Helper(root.left,root.val);
        int right = Helper(root.right,root.val);
        
        max = Math.Max(max,left+right);
        if(parent!=null && root.val == parent){
            return 1+Math.Max(left,right);
        }
        return 0;   
    }
}

Time Complexity: O(n)

Space Complexity: O(1)