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Count Tested Devices After Test Operations

Difficulty: Easy

Problem 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 specific operations based on the battery percentage of each device. The goal is to return the number of devices that will be tested after performing all operations.

Key Insights

  • Iterate through each device in the array.
  • Keep a count of devices tested based on their battery percentage.
  • If a device's battery percentage is greater than 0, decrease the battery percentage of all subsequent devices by 1, ensuring they don't go below 0.
  • Continue this process until all devices are checked.

Space and Time Complexity

Time Complexity: O(n^2) - In the worst case, each device could affect all subsequent devices. Space Complexity: O(1) - We are using a constant amount of extra space for counters and indices.

Solution

The algorithm uses a simple loop to iterate through the batteryPercentages array. For each device, it checks if the battery percentage is greater than 0. If it is, it increments a counter for tested devices and decreases the battery percentage of all subsequent devices by 1, ensuring no device's battery goes below 0. The final count of tested devices is returned at the end.

Code Solutions

def count_tested_devices(batteryPercentages):
    tested_count = 0
    n = len(batteryPercentages)
    
    for i in range(n):
        if batteryPercentages[i] > 0:
            tested_count += 1  # Increment tested devices count
            for j in range(i + 1, n):
                batteryPercentages[j] = max(0, batteryPercentages[j] - 1)  # Decrease battery percentage
                
    return tested_count
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