Pseudo_Palindromic_Paths_in_a_Binary_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 {
    int count;

    public int pseudoPalindromicPaths(TreeNode root) {
        count = 0;
        dfs(root, new int[10]);
        return count;
    }

    public void dfs(TreeNode node, int[] freq) {
        if (node == null) {
            return;
        }

        freq[node.val]++;
        if (node.left == null && node.right == null) {
            if (isPseudoPalindromic(freq)) {
                count++;
            }
        }

        dfs(node.left, freq);
        dfs(node.right, freq);
        freq[node.val]--;
    }

    public boolean isPseudoPalindromic(int[] freq) {
        int oddCount = 0;
        for (int i = 1; i <= 9; i++) {
            if (freq[i] % 2 != 0) {
                oddCount++;
            }
        }
        return oddCount <= 1;
    }
}