LeetCode 1394. Find Lucky Integer in an Array找出数组中的幸运数【Easy】【Python】【暴力】

Problem

LeetCode

Given an array of integers arr, a lucky integer is an integer which has a frequency in the array equal to its value.

Return a lucky integer in the array. If there are multiple lucky integers return the largest of them. If there is no lucky integer return -1.

Example 1:

Input: arr = [2,2,3,4]
Output: 2
Explanation: The only lucky number in the array is 2 because frequency[2] == 2.

Example 2:

Input: arr = [1,2,2,3,3,3]
Output: 3
Explanation: 1, 2 and 3 are all lucky numbers, return the largest of them.

Example 3:

Input: arr = [2,2,2,3,3]
Output: -1
Explanation: There are no lucky numbers in the array.

Example 4:

Input: arr = [5]
Output: -1

Example 5:

Input: arr = [7,7,7,7,7,7,7]
Output: 7

Constraints:

  • 1 <= arr.length <= 500
  • 1 <= arr[i] <= 500

问题

力扣

在整数数组中,如果一个整数的出现频次和它的数值大小相等,我们就称这个整数为「幸运数」。

给你一个整数数组 arr,请你从中找出并返回一个幸运数。

  • 如果数组中存在多个幸运数,只需返回 最大 的那个。
  • 如果数组中不含幸运数,则返回 -1 。

示例 1:

输入:arr = [2,2,3,4]
输出:2
解释:数组中唯一的幸运数是 2 ,因为数值 2 的出现频次也是 2 。

示例 2:

输入:arr = [1,2,2,3,3,3]
输出:3
解释:1、2 以及 3 都是幸运数,只需要返回其中最大的 3 。

示例 3:

输入:arr = [2,2,2,3,3]
输出:-1
解释:数组中不存在幸运数。

示例 4:

输入:arr = [5]
输出:-1

示例 5:

输入:arr = [7,7,7,7,7,7,7]
输出:7

提示:

  • 1 <= arr.length <= 500
  • 1 <= arr[i] <= 500

思路

暴力

自定义排序,然后暴力求解。
Python3代码
from typing import List
import collections

class Solution:
    def findLucky(self, arr: List[int]) -> int:
        cnt = collections.Counter(arr)
        # 先按频次排序,再按数值大小排序
        res = sorted(cnt.items(), key=lambda x:(x[1],x[0]), reverse=True)
        for i in range(len(res)):
            # 频次等于数值大小
            if res[i][0] == res[i][1]:
                return res[i][0]
        return -1

GitHub链接

Python