1394. Find Lucky Integer in an Array --------------E

Q:

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

A:

class Solution {
public:
    int findLucky(vector<int>& arr) {
        int lucky = -1;
        unordered_map<int, int> countMap;
        for(auto val : arr){
            countMap[val] += 1;
        }
        vector<int> luckies;
        auto iter = countMap.begin();
        while(iter!= countMap.end()){
            if(iter->second == iter->first)
                luckies.push_back(iter->first);            
            iter++;
        }
        if(luckies.size()>0){
            lucky = *max_element(luckies.begin(), luckies.end());
        }
        return lucky;
    }
};