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;

        HashMap<Integer, int[]> map = new HashMap<>();
        dfs(root, map, 1, 1);
        int res = 0;
        for (HashMap.Entry<Integer, int[]> e : map.entrySet()) {
            res = Math.max(res, e.getValue()[1] - e.getValue()[0] + 1);
        }

        return res;
    }
    private void dfs(TreeNode root, HashMap<Integer, int[]> map, int curId, int depth) {
        if (!map.containsKey(depth)) map.put(depth, new int[] {Integer.MAX_VALUE, Integer.MIN_VALUE});
        map.get(depth)[0] = Math.min(map.get(depth)[0], curId);
        map.get(depth)[1] = Math.max(map.get(depth)[1], curId);

        if (root.left != null) {
            dfs(root.left, map, curId * 2, depth + 1);
        }
        if (root.right != null) {
            dfs(root.right, map, curId * 2 + 1, depth + 1);
        }
    }
}