Java – Is This Code Efficient for Finding Array Max?

java

I am trying to find max value of an array, firstly i am shorting my array min to max after that i am using array[array.length-1] Is this logic efficient in large arrays?

public static int findMax(int[] array){

    Arrays.sort(array);

    int max = array[array.length-1];

    return max;
}//end method

Best Answer

No it's not.

Arrays.sort(array);

That line alone has an O(nlogn) running time. It can result in as many iterations as n, where n is the number of elements in the array, multiplied by log base 2 of n.

It would be much faster to just iterate through the array once.

public static int findMax(int[] array) {
    int indexOfMax = 0;
    for (i=1; i < array.length; i++) {
        if (array[i] > array[indexOfMax] {
            indexOfMax = i;
    }
    return indexOfMax
}

That has a maximum running time as O(n).

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Java – Object-Oriented Class Design

Example 2 is quite bad for testing... and I don't mean that you can't test the internals. You also can't replace your XmlReader object by a mock object as you have no object at all.

Example 1 is needlessly hard to use. What about

XmlReader reader = new XmlReader(url);
Document result = reader.getDocument();

which is not any harder to use than your static method.

Things like opening the URL, reading XML, converting bytes to strings, parsing, closing sockets, and whatever, are uninteresting. Creating an object and using it is important.

So IMHO the proper OO Design is to make just the two things public (unless you really need the intermediate steps for some reason). Static is evil.

Java – How to Transition from JavaScript to Java

Using arrays for everything is a bad idea. Even in JavaScript. But in Java even more so, because arrays are far more narrow in Java.

The elements of your return array are in fact representing results. You should communicate it accordingly:

class Result {
     public int someInt;//no idea what this actually is, but a class will allow you giving it a proper name
     public String someString;//same as with the other field. Also, I suppose String is actually wrong here, since it rather looks like a '-'-separated list of integers, which should rather be represented as an array of integers
     Result(String someString, int someInt) {
           this.someString = someString;
           this.someInt = someInt;
     }
}

And then your return value should look something like:

ArrayList.ofList(new Result('1-3-5', 50), new Result('2-5-8', 90), new Result('2-4-7', 75))

Best Answer

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