LeetCode: 662. Maximum Width of Binary Tree binary maximum width

试题：
Given a binary tree, write a function to get the maximum width of the given tree. The width of a tree is the maximum width among all levels. The binary tree has the same structure as a full binary tree, but some nodes are null.

The width of one level is defined as the length between the end-nodes (the leftmost and right most non-null nodes in the level, where the null nodes between the end-nodes are also counted into the length calculation.

Example 1:

Input:

       1
     /   \
    3     2
   / \     \  
  5   3     9 

Output: 4
Explanation: The maximum width existing in the third level with the length 4 (5,3,null,9).
Example 2:

Input:

      1
     /  
    3    
   / \       
  5   3     

Output: 2
Explanation: The maximum width existing in the third level with the length 2 (5,3).
Example 3:

Input:

      1
     / \
    3   2 
   /        
  5      

Output: 2
Explanation: The maximum width existing in the second level with the length 2 (3,2).
Example 4:

Input:

      1
     / \
    3   2
   /     \  
  5       9 
 /         \
6           7

Output: 8
Explanation:The maximum width existing in the fourth level with the length 8 (6,null,null,null,null,null,null,7).

Code:
first thought to get width, need to know the current position of each node is located, the position reference may be calculated exhaust stack 2n + 1,2n + 2; then all nodes in order to calculate the same level, a level required to record the current node level, and using non-recursive binary tree traversal.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class MarkNode{
    TreeNode node;
    int level, pos;
    MarkNode(TreeNode n, int l, int p){
        node = n;
        level = l;
        pos = p;
    }
}

class Solution {
    public int widthOfBinaryTree(TreeNode root) {
        Queue<MarkNode> queue = new LinkedList<>();
        queue.offer(new MarkNode(root, 1, 0));
        int curLevel = 1, left = 0, max = 0;
        while(!queue.isEmpty()){
            MarkNode curNode = queue.poll();
            if(curNode.level != curLevel){
                curLevel = curNode.level;
                left= curNode.pos;
            }else{
                max = Math.max(max, curNode.pos - left + 1);
            }
            if(curNode.node.left != null){
                queue.offer(new MarkNode(curNode.node.left, curNode.level + 1, curNode.pos * 2 + 1));
            }
            if(curNode.node.right != null){
                queue.offer(new MarkNode(curNode.node.right, curNode.level + 1, curNode.pos * 2 + 2));
            }
        }
        return max;
    }

}