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2460. Apply Operations to an Array 👍

Approach 1: No Swap

  • Time: $O(n)$
  • Space: $O(n)$
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class Solution {
 public:
  vector<int> applyOperations(vector<int>& nums) {
    vector<int> ans(nums.size());

    for (int i = 0; i + 1 < nums.size(); ++i)
      if (nums[i] == nums[i + 1]) {
        nums[i] *= 2;
        nums[i + 1] = 0;
      }

    int i = 0;
    for (const int num : nums)
      if (num > 0)
        ans[i++] = num;

    return ans;
  }
};

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class Solution {
  public int[] applyOperations(int[] nums) {
    int[] ans = new int[nums.length];

    for (int i = 0; i + 1 < nums.length; ++i)
      if (nums[i] == nums[i + 1]) {
        nums[i] *= 2;
        nums[i + 1] = 0;
      }

    int i = 0;
    for (final int num : nums)
      if (num > 0)
        ans[i++] = num;

    return ans;
  }
}

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

    for i in range(len(nums) - 1):
      if nums[i] == nums[i + 1]:
        nums[i] *= 2
        nums[i + 1] = 0

    i = 0
    for num in nums:
      if num > 0:
        ans[i] = num
        i += 1

    return ans

Approach 2: Swap

  • Time: $O(n)$
  • Space: $O(n)$
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class Solution {
 public:
  vector<int> applyOperations(vector<int>& nums) {
    for (int i = 0, j = 0; i < nums.size(); ++i) {
      if (i + 1 < nums.size() && nums[i] == nums[i + 1]) {
        nums[i] *= 2;
        nums[i + 1] = 0;
      }
      if (nums[i] > 0)
        swap(nums[i], nums[j++]);
    }
    return nums;
  }
};

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class Solution {
  public int[] applyOperations(int[] nums) {
    for (int i = 0, j = 0; i < nums.length; ++i) {
      if (i + 1 < nums.length && nums[i] == nums[i + 1]) {
        nums[i] *= 2;
        nums[i + 1] = 0;
      }
      if (nums[i] > 0) {
        swap(nums, i, j++);
      }
    }
    return nums;
  }

  private void swap(int[] nums, int i, int j) {
    final int temp = nums[i];
    nums[i] = nums[j];
    nums[j] = temp;
  }
}

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class Solution:
  def applyOperations(self, nums: list[int]) -> list[int]:
    j = 0
    for i in range(len(nums)):
      if i + 1 < len(nums) and nums[i] == nums[i + 1]:
        nums[i] *= 2
        nums[i + 1] = 0
      if nums[i] > 0:
        nums[i], nums[j] = nums[j], nums[i]
        j += 1
    return nums