Count Univalue Subtrees

Given a binary tree, count the number of uni-value subtrees.

A Uni-value subtree means all nodes of the subtree have the same value.

For example:
Given binary tree,

              5
             / \
            1   5
           / \   \
          5   5   5

return 4.

Recursion.

public class CountUnivalueSubtrees {
    int count = 0;
    public int countUnivalSubtrees(TreeNode root) {
        if (root == null) {
            return count;
        }
        validTree(root);
        return count;
    }

    private boolean validTree(TreeNode root) {
        if (root == null) {
            return true;
        }
        if (root.left == null || root.right == null) {
            count++;
            return true;
        }
        boolean left = validTree(root.left);
        boolean right = validTree(root.right);
        if (left && right
            && ( (root.left == null && root.val == root.right.val)
                || (root.right == null && root.val == root.left.val)
                || (root.val == root.left.val && root.val == root.right.val)
        )) {
            count++;
            return true;
        }
        return false;
    }
}