CODE

/**
* Definition for a binary tree node.
* public class TreeNode {
*     public int val;
*     public TreeNode left;
*     public TreeNode right;
*     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
*         this.val = val;
*         this.left = left;
*         this.right = right;
*     }
* }
*/

public class Solution {
  bool b = true;
  int[] nodes = new int[1000];
  public bool IsBalanced(TreeNode root) {
    for (int i = 0; i < 1000; i++)
      nodes[i] = -1;
    traversal(root);
    if (!b) return false;
    return true;
  }

  int nodeNum = -1;
  int traversal(TreeNode r)
  {
    nodeNum++;
    if (r == null)
      return 0;
    
    int left = traversal(r.left);
    int right = traversal(r.right);

    if (Math.Abs(left - right) > 1)
      b = false;
    nodes[nodeNum] = Math.Max(left, right);
    return nodes[nodeNum] + 1;
  }
}