2576. Find the Maximum Number of Marked Indices
You are given a 0-indexed integer array nums.
Initially, all of the indices are unmarked. You are allowed to make this operation any number of times:
- Pick two different unmarked indices
iandjsuch that2 * nums[i] <= nums[j], then markiandj.
Return the maximum possible number of marked indices in nums using the above operation any number of times.
Example 1:
Input: nums = [3,5,2,4] Output: 2 Explanation: In the first operation: pick i = 2 and j = 1, the operation is allowed because 2 * nums[2] <= nums[1]. Then mark index 2 and 1. It can be shown that there's no other valid operation so the answer is 2.
Example 2:
Input: nums = [9,2,5,4] Output: 4 Explanation: In the first operation: pick i = 3 and j = 0, the operation is allowed because 2 * nums[3] <= nums[0]. Then mark index 3 and 0. In the second operation: pick i = 1 and j = 2, the operation is allowed because 2 * nums[1] <= nums[2]. Then mark index 1 and 2. Since there is no other operation, the answer is 4.
Example 3:
Input: nums = [7,6,8] Output: 0 Explanation: There is no valid operation to do, so the answer is 0.
Constraints:
1 <= nums.length <= 1051 <= nums[i] <= 109
ArrayTwo PointersBinary SearchGreedySorting
Hints
Hint 1
Think about how to check that performing k operations is possible.
Hint 2
To perform k operations, it’s optimal to use the smallest k elements and the largest k elements and think about how to match them.
Hint 3
It’s optimal to match the ith smallest number with the k-i + 1 largest number.
Hint 4
Now we need to binary search on the answer and find the greatest possible valid k.
Preparing judge…