10031. Count Tested Devices After Test Operations

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.

class Solution {
public:
    int countTestedDevices(vector<int>& batteryPercentages) {
        int res = 0, pre = 0;
        for(auto& x : batteryPercentages) {
            x -= pre;
            if(x > 0) {
                res += 1;
                pre += 1;
            }
        }
        return res;
    }
};