[leetcode] Balanced Binary Tree

/*
 *  be careful about the order of traversal!!!don‘t do recursion in recursion that resulting traverse the tree many times.
 *      so we need to return the height and isBalanced of a node at the same time, but we can only return one, so if we use C++
 *      we can use reference, but it‘s java... so we have to wrap a primitive or using an array.
 * https://oj.leetcode.com/discuss/3931/can-we-have-a-better-solution
 * http://www.cnblogs.com/remlostime/archive/2012/10/27/2742987.html
 * 
 */
public class Solution {

    public boolean isBalanced(TreeNode root) {
        Height height = new Height();
        return checkBalanced(root, height);
    }

    private boolean checkBalanced(TreeNode root, Height h) {
        if (root == null) {
            h.height = 0;
            return true;
        }
        Height lh = new Height();
        Height rh = new Height();
        boolean leftBalanced = checkBalanced(root.left, lh);
        boolean rightBalanced = checkBalanced(root.right, rh);
        h.height = Math.max(lh.height, rh.height) + 1;

        return leftBalanced && rightBalanced && (Math.abs(lh.height - rh.height) <= 1);
    }

    public static void main(String[] args) {
        TreeNode root = new TreeNode(5);
        root.right = new TreeNode(7);
        root.right.left = new TreeNode(3);
        root.right.left.right = new TreeNode(3);
        root.left = new TreeNode(3);

        System.out.println(new Solution().isBalanced(root));
    }

    private static class Height {
        int height;
    }

}