1394. Find Lucky Integer in an Array

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

这题利用map做一下就行了。

class FindLuckyIntegerInAnArray : public Solution {
public:
    void Exec() {

    }
    int findLucky(vector<int>& arr) {
        unordered_map<int, int> counts;
        for (auto v : arr) {
            auto it = counts.find(v);
            if (it == counts.end()) {
                counts.insert(std::make_pair(v, 1));
            } else {
                it->second++;
            }
        }
        int luckyNumber = -1;
        for (auto &pa : counts) {
            if (pa.second == pa.first) {
                if (pa.first > luckyNumber) {
                    luckyNumber = pa.first;
                }
            }
        }
        return luckyNumber;
    }
};