1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 class Solution {
11     public int widthOfBinaryTree(TreeNode root) {
12         if(root == null){
13             return 0;
14         }
15
16         LinkedList<Pair> que = new LinkedList<Pair>();
17         que.add(new Pair(root,1));
18         int curCount = 1;
19         int nextCount = 0;
20
21         int res = 1;
22         int start = 1;
23         int end = start;
24
25         while(!que.isEmpty()){
26             Pair cur = que.poll();
27             curCount--;
28             end = cur.id;
29
30             if(cur.node.left != null){
31                 que.add(new Pair(cur.node.left, cur.id*2));
32                 nextCount++;
33             }
34
35             if(cur.node.right != null){
36                 que.add(new Pair(cur.node.right, cur.id*2+1));
37                 nextCount++;
38             }
39
40             if(curCount == 0){
41                 res = Math.max(res, end-start+1);
42                 curCount = nextCount;
43                 nextCount = 0;
44                 start = que.isEmpty() ? 1 : que.peek().id;
45                 end = start;
46             }
47         }
48
49         return res;
50     }
51 }
52
53 class Pair{
54     TreeNode node;
55     int id;
56     public Pair(TreeNode node, int id){
57         this.node = node;
58         this.id = id;
59     }
60 }