Formatted question description: https://leetcode.ca/all/1481.html

1481. Least Number of Unique Integers after K Removals (Medium)

Given an array of integers arr and an integer k. Find the least number of unique integers after removing exactly k elements.

 

Example 1:

Input: arr = [5,5,4], k = 1
Output: 1
Explanation: Remove the single 4, only 5 is left.

Example 2:

Input: arr = [4,3,1,1,3,3,2], k = 3
Output: 2
Explanation: Remove 4, 2 and either one of the two 1s or three 3s. 1 and 3 will be left.

 

Constraints:

  • 1 <= arr.length <= 10^5
  • 1 <= arr[i] <= 10^9
  • 0 <= k <= arr.length

Related Topics:
Array, Sort

Solution 1.

// OJ: https://leetcode.com/problems/least-number-of-unique-integers-after-k-removals/

// Time: O(N + UlogU) where U is the number of unique counts
// Space: O(N)
class Solution {
public:
    int findLeastNumOfUniqueInts(vector<int>& A, int k) {
        unordered_map<int, int> cnt;
        for (int n : A) cnt[n]++;
        map<int, int> m;
        for (auto &p : cnt) m[p.second]++;
        int ans = cnt.size();
        for (auto &p : m) {
            int n = min(p.second, k / p.first);
            if (n == 0) break;
            ans -= n;
            k -= p.first * n;
        }
        return ans;
    }
};

Java

class Solution {
    public int findLeastNumOfUniqueInts(int[] arr, int k) {
        Map<Integer, Integer> numCountMap = new HashMap<Integer, Integer>();
        for (int num : arr) {
            int count = numCountMap.getOrDefault(num, 0) + 1;
            numCountMap.put(num, count);
        }
        List<Integer> list = new ArrayList<Integer>();
        Set<Integer> numSet = numCountMap.keySet();
        for (int num : numSet)
            list.add(numCountMap.get(num));
        int unique = 0;
        Collections.sort(list);
        int remain = arr.length - k;
        for (int i = list.size() - 1; i >= 0 && remain > 0; i--) {
            int count = list.get(i);
            remain -= count;
            unique++;
        }
        return unique;
    }
}

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