501_Find_Mode_in_Binary_Search_Tree.java

/*
501. Find Mode in Binary Search Tree
Difficulty: Easy 

501_Find_Mode_in_Binary_Search_Tree.java
*/

/**
 * 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[] findMode(TreeNode root) {
      
    List<Integer> ans = new ArrayList<>();
    int[] count = new int[2];

    inorder(root, count, ans);
    return ans.stream().mapToInt(Integer::intValue).toArray();
  }

  private TreeNode pred = null;

  private void inorder(TreeNode root, int[] count, List<Integer> ans) {
      
    if (root == null)
      return;

    inorder(root.left, count, ans);
    updateCount(root, count, ans);
    inorder(root.right, count, ans);
      
  }

  private void updateCount(TreeNode root, int[] count, List<Integer> ans) {
      
    if (pred != null && pred.val == root.val)
      ++count[0];
    else
      count[0] = 1;

    if (count[0] > count[1]) {
      count[1] = count[0];
      ans.clear();
      ans.add(root.val);
    } else if (count[0] == count[1]) {
      ans.add(root.val);
    }

    pred = root;
      
  }
}