题解 | #二叉树的最大宽度#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param root TreeNode类
     * @return int整型
     */
    public int widthOfBinaryTree (TreeNode root) {
        // write code here
        if (root == null) {
            return 0;
        }
        Deque<TreeNode> dq = new LinkedList<>();
        TreeNode cur = root;
        dq.offer(cur);
        int max = 0;
        while (!dq.isEmpty()) {
            while (!dq.isEmpty() && dq.peekFirst() == null) {
                dq.pollFirst();
            }
            while (!dq.isEmpty() && dq.peekLast() == null) {
                dq.pollLast();
            }
            int size = dq.size();
            max = Math.max(max, size);
            for (int i = 0; i < size; i++) {
                cur = dq.poll();
                if (cur != null) {
                    dq.offerLast(cur.left);
                    dq.offerLast(cur.right);
                } else {
                    dq.offerLast(null);
                    dq.offerLast(null);
                }
            }
        }
        return max;
    }
}