Question

2960. Count Tested Devices After Test Operations

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Description

You are given a 0-indexed integer array batteryPercentages having length n, denoting the battery percentages of n 0-indexed devices.

Your task is to test each device i in order from 0 to n - 1, by performing the following test operations:

• If batteryPercentages[i] is greater than 0:
  • Increment the count of tested devices.
  • Decrease the battery percentage of all devices with indices j in the range [i + 1, n - 1] by 1, ensuring their battery percentage never goes below 0, i.e, batteryPercentages[j] = max(0, batteryPercentages[j] - 1).
  • Move to the next device.
• Otherwise, move to the next device without performing any test.

Return _an integer denoting the number of devices that will be tested after performing the test operations in order._

 

Example 1:

Input: batteryPercentages = [1,1,2,1,3]
Output: 3
Explanation: Performing the test operations in order starting from device 0:
At device 0, batteryPercentages[0] > 0, so there is now 1 tested device, and batteryPercentages becomes [1,0,1,0,2].
At device 1, batteryPercentages[1] == 0, so we move to the next device without testing.
At device 2, batteryPercentages[2] > 0, so there are now 2 tested devices, and batteryPercentages becomes [1,0,1,0,1].
At device 3, batteryPercentages[3] == 0, so we move to the next device without testing.
At device 4, batteryPercentages[4] > 0, so there are now 3 tested devices, and batteryPercentages stays the same.
So, the answer is 3.

Example 2:

Input: batteryPercentages = [0,1,2]
Output: 2
Explanation: Performing the test operations in order starting from device 0:
At device 0, batteryPercentages[0] == 0, so we move to the next device without testing.
At device 1, batteryPercentages[1] > 0, so there is now 1 tested device, and batteryPercentages becomes [0,1,1].
At device 2, batteryPercentages[2] > 0, so there are now 2 tested devices, and batteryPercentages stays the same.
So, the answer is 2.

 

Constraints:

• 1 <= n == batteryPercentages.length <= 100
• 0 <= batteryPercentages[i] <= 100

Solutions

Solution 1: Simulation

Assume that the current number of devices we have tested is $ans$. When testing a new device $i$, its remaining battery is $\max(0, batteryPercentages[i] - ans)$. If the remaining battery is greater than $0$, it means this device can be tested, and we need to increase $ans$ by $1$.

Finally, return $ans$.

The time complexity is $O(n)$, where $n$ is the length of the array. The space complexity is $O(1)$.

class Solution:
  def countTestedDevices(self, batteryPercentages: List[int]) -> int:
    ans = 0
    for x in batteryPercentages:
      x -= ans
      ans += x > 0
    return ans

class Solution {
  public int countTestedDevices(int[] batteryPercentages) {
    int ans = 0;
    for (int x : batteryPercentages) {
      x -= ans;
      if (x > 0) {
        ++ans;
      }
    }
    return ans;
  }
}

class Solution {
public:
  int countTestedDevices(vector<int>& batteryPercentages) {
    int ans = 0;
    for (int x : batteryPercentages) {
      x -= ans;
      if (x > 0) {
        ++ans;
      }
    }
    return ans;
  }
};

func countTestedDevices(batteryPercentages []int) (ans int) {
  for _, x := range batteryPercentages {
    x -= ans
    if x > 0 {
      ans++
    }
  }
  return
}

function countTestedDevices(batteryPercentages: number[]): number {
  let ans = 0;
  for (let x of batteryPercentages) {
    x -= ans;
    if (x > 0) {
      ++ans;
    }
  }
  return ans;
}