Part (a)

Write the getChargeStartTime method that finds the optimal time to start charging.

Solution

public int getChargeStartTime(int chargeTime)
{
    int minCost = Integer.MAX_VALUE;
    int startTime = 0;
    
    for (int i = 0; i < 24; i++)
    {
        int cost = 0;
        for (int j = 0; j < chargeTime; j++)
        {
            cost += rate[(i + j) % 24];
        }
        if (cost < minCost)
        {
            minCost = cost;
            startTime = i;
        }
    }
    return startTime;
}

Part (b)

Alternative implementation using helper method.

Solution

// Using helper method getChargingCost:
public int getChargeStartTime(int chargeTime)
{
    int minCost = getChargingCost(0, chargeTime);
    int startTime = 0;
    
    for (int i = 1; i < 24; i++)
    {
        int cost = getChargingCost(i, chargeTime);
        if (cost < minCost)
        {
            minCost = cost;
            startTime = i;
        }
    }
    return startTime;
}

Key Concepts

Common Mistakes