Array Partition Python Solution with Tests

LeetCode 561, Easy. Topics: Array, Greedy, Sorting, Counting Sort. View on LeetCode. Generate this problem as a practice environment: tested reference solution, 20 parametrized pytest cases, and a playground notebook:

lcpy gen -n 561   # by problem number
lcpy gen -s array_partition   # by problem name

Problem

Given an integer array nums of 2n integers, group these integers into n pairs (a1, b1), (a2, b2), …, (an, bn) such that the sum of min(ai, bi) for all i is maximized. Return the maximized sum.

Examples

Input: nums = [1,4,3,2]
Output: 4

Explanation: All possible pairings (ignoring the ordering of elements) are:

(1, 4), (2, 3) -> min(1, 4) + min(2, 3) = 1 + 2 = 3
(1, 3), (2, 4) -> min(1, 3) + min(2, 4) = 1 + 2 = 3
(1, 2), (3, 4) -> min(1, 2) + min(3, 4) = 1 + 3 = 4 So the maximum possible sum is 4.

Input: nums = [6,2,6,5,1,2]
Output: 9

Explanation: The optimal pairing is (2, 1), (2, 5), (6, 6). min(2, 1) + min(2, 5) + min(6, 6) = 1 + 2 + 6 = 9.

Constraints

1 <= n <= 10^4
nums.length == 2 * n
-10^4 <= nums[i] <= 10^4

Solution

Reference implementation from solution.py on GitHub, full suite in test_solution.py:

class Solution:
    # Time: O(n log n)
    # Space: O(n) for the sort
    def array_pair_sum(self, nums: list[int]) -> int:
        nums.sort()
        return sum(nums[::2])

Complexity

Time	Space
O(n log n)	O(n) for the sort

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Array Partition Python Solution with Tests

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