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3507. Minimum Pair Removal to Sort Array I 👍

  • Time: $O(n^2)$
  • Space: $O(n)$
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#include <ranges>

class Solution {
 public:
  int minimumPairRemoval(vector<int>& nums) {
    int ans = 0;

    while (hasInversion(nums)) {
      vector<int> pairSums;
      for (const auto& [a, b] : views::pairwise(nums))
        pairSums.push_back(a + b);
      const int minPairSum = ranges::min(pairSums);
      const int minPairIndex =
          ranges::find(pairSums, minPairSum) - pairSums.begin();
      nums[minPairIndex] = minPairSum;
      nums.erase(nums.begin() + minPairIndex + 1);
      ++ans;
    }

    return ans;
  }

 private:
  bool hasInversion(const vector<int>& nums) {
    for (const auto& [a, b] : views::pairwise(nums))
      if (a > b)
        return true;
    return false;
  }
};

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class Solution {
  public int minimumPairRemoval(int[] nums) {
    int ans = 0;
    List<Integer> numsList = Arrays.stream(nums).boxed().collect(Collectors.toList());

    while (hasInversion(numsList)) {
      List<Integer> pairSums = new ArrayList<>();
      for (int i = 0; i < numsList.size() - 1; ++i)
        pairSums.add(numsList.get(i) + numsList.get(i + 1));
      int minPairSum = Integer.MAX_VALUE;
      int minPairIndex = -1;
      for (int i = 0; i < pairSums.size(); ++i)
        if (pairSums.get(i) < minPairSum) {
          minPairSum = pairSums.get(i);
          minPairIndex = i;
        }
      numsList.set(minPairIndex, minPairSum);
      numsList.remove(minPairIndex + 1);
      ++ans;
    }

    return ans;
  }

  private boolean hasInversion(List<Integer> nums) {
    for (int i = 0; i < nums.size() - 1; ++i)
      if (nums.get(i) > nums.get(i + 1))
        return true;
    return false;
  }
}

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class Solution:
  def minimumPairRemoval(self, nums: list[int]) -> int:
    ans = 0

    while any(x > y for x, y in itertools.pairwise(nums)):
      pairSums = [x + y for x, y in itertools.pairwise(nums)]
      minPairSum = min(pairSums)
      minPairIndex = pairSums.index(minPairSum)
      nums[minPairIndex] = minPairSum
      nums.pop(minPairIndex + 1)
      ans += 1

    return ans