1338. Reduce Array Size to The Half

Problem

You are given an integer array arr. You can choose a set of integers and remove all the occurrences of these integers in the array.

Return the minimum size of the set so that at least half of the integers of the array are removed.

https://leetcode.cn/problems/reduce-array-size-to-the-half/

Example 1:

Input: arr = [3,3,3,3,5,5,5,2,2,7]
Output: 2
Explanation: Choosing {3,7} will make the new array [5,5,5,2,2] which has size 5 (i.e equal to half of the size of the old array).
Possible sets of size 2 are {3,5},{3,2},{5,2}.
Choosing set {2,7} is not possible as it will make the new array [3,3,3,3,5,5,5] which has a size greater than half of the size of the old array.

Example 2:

Input: arr = [7,7,7,7,7,7]
Output: 1
Explanation: The only possible set you can choose is {7}. This will make the new array empty.

Constraints:

• 2 <= arr.length <= 10⁵
• arr.length is even.
• 1 <= arr[i] <= 10⁵

Test Cases

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class Solution:
    def minSetSize(self, arr: List[int]) -> int:

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import pytest

from solution import Solution


@pytest.mark.parametrize('arr, expected', [
    ([3,3,3,3,5,5,5,2,2,7], 2),
    ([7,7,7,7,7,7], 1),

    ([1,9], 1),
])
class Test:
    def test_solution(self, arr, expected):
        sol = Solution()
        assert sol.minSetSize(arr) == expected

Thoughts

统计 arr 中每个不同数字出现的次数，对这些次数倒排序，从次数最多的开始取，直到大于等于 arr 长度的一半即可。

Code

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from collections import Counter


class Solution:
    def minSetSize(self, arr: list[int]) -> int:
        counts = sorted(Counter(arr).values(), reverse=True)
        m = len(arr) >> 1
        for i, freq in enumerate(counts, 1):
            m -= freq
            if m <= 0:
                return i

许可协议

本文除了题目描述（Problem）部分之外，其他内容由 Calf 原创，采用 CC BY-NC-SA 4.0 许可协议，转载请注明出处。

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