计算数组中的最大值和最小值

Question

I have an array of integers and need to find the position in the array of the maximum number along with the minimum. I have it working but it doesn't seem to be a very good way to do it. Can anyone suggest a better way to achieve what I have?

Here's my code:

int[] usageHours = { 3, 3, 5, 4, 0, 0, 2, 2, 4, 25, 158, 320, 212, 356, 401, 460, 480, 403, 298, 213, 102, 87, 34, 45 };
double myAverage = usageHours.Average();
int runningTotal = 0;
int runningMaxPosition = 0;

for (int i = 0; i < usageHours.Length; i++)
{
    if (usageHours[i] > runningTotal)
    {
        runningMaxPosition = i;
        runningTotal = usageHours[i];
    }
}

txtmax.Text = Convert.ToString(runningMaxPosition)+" With: "+Convert.ToString(runningTotal)+" Users";
txtAv.Text = Convert.ToString(myAverage);

Answer 1

That code is mostly fine. I'd suggest changing the variable names a bit, but that's all. You can work out the minimum in the same loop. I've changed the "if" conditions very slightly to guarantee that they always pick out at least one element (even if all the values are, say, int.MinValue ). There are other ways of approaching this, but this is one example. If you have an empty array, you'll end up with max=min=0, and both indexes=-1.

int currentMax = 0;
int currentMaxIndex = -1;
int currentMin = 0;
int currentMinIndex = -1;

for (int i = 0; i < usageHours.Length; i++)
{
    if (currentMaxIndex == -1 || usageHours[i] > currentMax)
    {
        currentMaxIndex = i;
        currentMax = usageHours[i];
    }
    if (currentMinIndex == -1 || usageHours[i] < currentMin)
    {
        currentMinIndex = i;
        currentMin = usageHours[i];
    }
}

Here's an alternative using nullable value types to represent "there were no values" answers:

int currentMax? = null;
int currentMaxIndex? = null;
int currentMin? = null;
int currentMinIndex? = null;

for (int i = 0; i < usageHours.Length; i++)
{
    if (currentMax == null || usageHours[i] > currentMax.Value)
    {
        currentMax = i;
        currentMax = usageHours[i];
    }
    if (currentMin == null || usageHours[i] < currentMin.Value)
    {
        currentMinIndex = i;
        currentMin = usageHours[i];
    }
}

Don't worry if you haven't come across nullable value types yet though...

Answer 2

The code looks OK for finding the max value. If you are using C# 3 or later you could use the LINQ extension methods (there are Min , Max and Average methods, and on List there is also a FindIndex method, amongst others), but I get the impression that you are learning programming, and then it is sometimes a good idea to implement stuff that may be built into the framework, just for the learning value.

Answer 3

I just wanted to provide one-liner solution for the question (for completeness). In the OP's original question he only asks for index of the maximum and index of the minimum.

Let's stick to this question. This is the most interesting question because to find maximum value we can simply use Enumerable.Max LINQ method. The same goes for Min and Average.

Let's only provide index of the max, index of min can be retrieved with similar code.

int indexOfMax = Enumerable.Range(0, usageHours.Length).Aggregate(
    (indexOfMax, i) => (usageHours[i] > usageHours[indexOfMax] ? i : indexOfMax)
);

Delegate inside of Aggregate's brackets is executed for each index of array. It gets as parameters "index of maximum value so far found", and current index. It returns "index of maximum value so far found". Obviously in each iteration "index of maximum value so far found" will only change to current index if corresponding element of array is greater than previous maximum.

Answer 4

scratch the linq code, it didnt work the way you wanted

you could make your code a little bit more concise

for (int i = 0; i < usageHours.Length; i++)
{
    if (usageHours[i] > usageHours[runningMaxPosition])
        runningMaxPosition = i;
}

all it does differently is leavs out the temporary runningTotal variable.

Answer 5

How about this:

double average = usageHours.Average();
int maxPosition = Enumerable.Range(0, usageHours.Length).Max(i => usageHours[i]);
int minPosition = Enumerable.Range(0, usageHours.Length).Min(i => usageHours[i]);

Answer 6

Your code isn't bad, but it won't work if all the values are less than zero.

Try this:

int getArrayMaxPosition (double[] theArray) 
{    
    double maxVal = theArray[0];
    int ret = 0;
    int currentIndex = 0;

    foreach (double aValue in theArray) 
    {
        if (aValue > maxVal)
        {
             ret = currentIndex;
             maxVal = avalue;
        }
        currentIndex++;
    }

    return ret;
 }

Answer 7

As was mentioned on the comment's to Jon's answer, Jon's solution really is the best, most direct, quickest way of doing it.

If, however, you did want to use Igor's solution, here's the rest of it (to get the actual positions as well as the values):

int maxValue = Enumerable.Range(0, usageHours.Length).Max(i => usageHours[i]);
int maxPosition = Array.FindIndex(usageHours, i => i == maxValue);
int minValue = Enumerable.Range(0, usageHours.Length).Min(i => usageHours[i]);
int minPosition = Array.FindIndex(usageHours, i => i == minValue);