leetcode1394. Find Lucky Integer in an Array

Posted 2020-11-27 seyjs

题目如下：

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

解题思路：非常简单的题目。

代码如下：

class Solution(object):
    def findLucky(self, arr):
        """
        :type arr: List[int]
        :rtype: int
        """
        val = [0] * 501
        for i in arr:
            val[i] += 1
        for inx in range(len(val)-1,0,-1):
            if inx == val[inx]:
                return inx
        return -1