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.

Solution:

public int countUnivalSubtrees(TreeNode root) {
    int[] count = new int[1];
    isUnivalSubtrees(root, count);
    return count[0];
}

public boolean isUnivalSubtrees(TreeNode root, int[] count) {
    if (root == null) {
        return false;
    }
    boolean left = isUnivalSubtrees(root.left, count);
    boolean right = isUnivalSubtrees(root.right, count);
    if (!left && !right) {
        if (root.left == null && root.right == null) {
            count[0]++;
            return true;
        }
    } else if (left && right) {
        if (root.left.val == root.val && root.right.val == root.val) {
            count[0]++;
            return true;
        }
    } else if (left && !right) {
        if (root.right == null && root.left.val == root.val) {
            count[0]++;
            return true;
        }
    } else if (!left && right) {
        if (root.left == null && root.right.val == root.val) {
            count[0]++;
            return true;
        }
    }
    return false;
}

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