Finding minimum integer in ArrayList without collections

Question

I'm trying to find the smallest integer in an ArrayList just by using two simple for loops. I tried originally with one for loop, but it wasn't updating correctly. I haven't learned collections yet, so this should be done without using any collections code.

This is what I have:

public static void printInOrder(ArrayList<Integer> data){

 int minIndex = 0 ;
 for(int i = 0; i < data.size(); i++){
   minIndex = i;
   for(int j = i + 1; j < data.size() - 1; j++){
     if(data.get(j) < data.get(minIndex)){
       minIndex = j;}

   }
   System.out.println(data.get(minIndex) + " ");
 }
}//printInOrder

My minimum always seems to be the last value in the list, so I tried printing the data.get(minIndex) in the first for loop to see what happens, and it seems to update it different values, and then finally, the last value. I have no idea why this is happening.

This is what it's printing for example:

Original list: [47, 19, 46, 42, 15, 26, 36, 27, 13, 15, 1, 40, 34, 14, 6, 34, 28, 12, 15, 13] Print the minimum: 1 1 1 1 1 1 1 1 1 1 1 6 6 6 6 12 12 12 15 13

You don't need double loop.. A single loop should do it as long as you are keeping the current minimum — gtgaxiola
– gtgaxiola, Commented Apr 9, 2015 at 18:51
@gtgaxiola, if I tried it with a single loop, what would I compare in my if statement? Because I tried that way for a while, but it too wasn't giving me the correct minimum. — user180708
– user180708, Commented Apr 9, 2015 at 18:55
Your code currently successfully finds the smallest number of the list starting at i, for all starting indices i. You wanted to find the smallest number of the list starting at 0 only. — that other guy
– that other guy, Commented Apr 9, 2015 at 19:00

theguywhodreams · Accepted Answer · 2015-04-09 19:08:03Z

3

You can do this quick solution if you want to avoid using Collections.

public static void printInOrder(ArrayList<Integer> data){

    Integer[] array = (Integer[]) data.toArray();
    Arrays.sort(array);
    System.out.println(array[0]);

}

The smallest integer would always be at index 0 in this case.

Or, if you do want to go through the whole ArrayList using a loop, I'd suggest you store the actual value in a variable instead of the index. Doing so, you get:

public static void printInOrder(ArrayList<Integer> data){

    int minInteger = data.get(0);
    for(int i = 1; i < data.size(); i++){
        if(data.get(i) < minInteger) minInteger= data.get(i);
    }
    System.out.println(minInteger);

}

edited Apr 9, 2015 at 19:08

answered Apr 9, 2015 at 18:52

theguywhodreams

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2 Comments

Paul Boddington Over a year ago

Integer[] array = data.toArray(); doesn't compile.

theguywhodreams Over a year ago

My bad, forgot to cast. :)

user4266318 · Accepted Answer · 2015-04-09 18:57:45Z

0

You're not supposed to do sorting to find the minimum

Here's the code

public static void Min(int arr[])
{
   int min = arr[0];
    int i=0;
while(i<arr.length)
 {
        if (arr[i] < min) {
            min=arr[i];
        }
    }
    return min;
}

answered Apr 9, 2015 at 18:57

user4266318

3 Comments

user4266318 Over a year ago

Well , if you are interested in sorting and then find the minimum no problem but the issue was it didn't make a sense and i think it takes up double time to find you a minimum with a single min algo

theguywhodreams Over a year ago

Well by analysis, a linear search would have a complexity of O(n), having n iterations worst-case. Using Java's built-in sorting function, it runs at O(n log n), and getting the minimum after that would be O(1) for sure. This, way, I don't think it's as inefficient as it may seem.

Durandal Over a year ago

@theguywhodreams Thats one way to look at it, the other is that log2(1024) already works out to 10, so sorting 1024 elements to find the minimum has approximately 10 times the complexity of the linear search. If that is to be considered efficient (enough) or not is highly dependend on the actual use case.

Amir Afghani · Accepted Answer · 2015-04-09 19:00:14Z

0

Untested:

public static int calculateMinIndex(final ArrayList<Integer> data) {
    int minIndex = 0;
    for(int i = 0; i < data.size() - 1; i++) {
        if(data.get(i) > data.get(i+1)) {
            minIndex = i+1;
        }
    }
    return minIndex;
}

answered Apr 9, 2015 at 19:00

Amir Afghani

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