3634. Minimum Removals to Balance Array

Time: O(n)

Space: O(n)

Approach

Precompute prefix min-max and suffix min-max; find min removals where left max < right min.

Key Techniques

Array problems involve manipulating elements stored in a contiguous block of memory. Key techniques include two-pointer traversal, prefix sums, sliding windows, and in-place partitioning. In C#, arrays are zero-indexed and fixed in size — use List<T> when you need dynamic resizing.

Greedy

Greedy algorithms make locally optimal choices at each step, hoping to reach a global optimum. Greedy works when a problem has the "greedy choice property" and "optimal substructure". Common applications: interval scheduling, activity selection, Huffman coding, and jump game.

3634.cs

// Approach: Precompute prefix min-max and suffix min-max; find min removals where left max < right min.
// Time: O(n) Space: O(n)

public class Solution
{
    public int MinRemoval(int[] nums, int k)
    {
        Array.Sort(nums);
        int cnt = 0;
        int n = nums.Length;
        for (int i = 0; i < n; ++i)
        {
            int j = n;
            if ((long)nums[i] * k <= nums[n - 1])
            {
                j = Array.BinarySearch(nums, nums[i] * k + 1);
                j = j < 0 ? ~j : j;
            }
            cnt = Math.Max(cnt, j - i);
        }

        return n - cnt;
    }
}

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