Find the Maximum Number of Marked Indices
Problem Statement - link #
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 i and j such that 2 * nums[i] <= nums[j], then mark i and j.
Return the maximum possible number of marked indices in nums using the above operation any number of times.
Examples #
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 <= 10^51 <= nums[i] <= 10^9
Solutions #
class Solution {
public:
int maxNumOfMarkedIndices(vector<int>& nums) {
int n = nums.size(), res = 0;
int i = 0, j = n / 2;
sort(nums.begin(), nums.end());
while(i < n/2 && j < n) {
if(nums[i] * 2 <= nums[j]) {
res += 2;
i++, j++;
}
else {
j++;
}
}
return res;
}
};