[leetcode] 1394. Find Lucky Integer in an Array

Description

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 <= 5001 <= arr[i] <= 500

分析

题目的意思是：给你一个数组，找出频率等于数值的数，返回最大的那一个，如果没有，则返回-1.思路也很直接，用字典统计一下每个数的频率，然后遍历一次找到最大值就行了

代码

class Solution: def findLucky(self, arr: List[int]) -> int: d=collections.defaultdict(list) for item in arr: d[item].append(item) lucky=-1 for k,v in d.items(): if(k==len(v) and lucky<k): lucky=k return lucky