题解 | #二叉树的最大宽度#

层序遍历改造

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) {
        if (root == null) return 0;
        LinkedList<Node> queue = new LinkedList<>();
        queue.add(new Node(root, 0));
        int maxWidth = 0;
        while (!queue.isEmpty()) {
            int size = queue.size();
            int firstIndex = queue.peekFirst().pos, lastIndex = queue.peekLast().pos;
            maxWidth = Math.max(maxWidth, lastIndex - firstIndex + 1);
            for (int i = 0; i < size; i++) {
                Node node = queue.poll();
                if (node.root.left != null) {
                    queue.add(new Node(node.root.left, node.pos << 1));
                }
                if (node.root.right != null) {
                    queue.add(new Node(node.root.right, (node.pos << 1) | 1));
                }
            }
        }
        return maxWidth;
    }
    class Node {
        TreeNode root;
        int pos;

        public Node(TreeNode root, int pos) {
            this.root = root;
            this.pos = pos;
        }
    }
}