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Big O notation for an array

Posted on 2009-07-05
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Last Modified: 2013-11-23
Hi,

What is the complexity of an array for getting an element using index like a[10].
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Question by:SunScreenCert
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7 Comments
 
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Thomas4019 earned 500 total points
ID: 24781766
The complexity is O(1) as it takes the exact smae amount of time to access an element regardless of the size of the list.
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Expert Comment

by:a_b
ID: 24782553
Since you the index number that you want to address you donot have to traverse the array you can directly access it without looping through the array, so it is just one operation, therefore O(1).

It would be a different story if you had to access maybe the largest or the smallest element of the array.
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by:SunScreenCert
ID: 24782738
I asked this question coz somebody was suggesting that this program be split into different arrays. Please tell me if this would give me any additional advantage. Also i am novice to programming, so all tips to make it efficient and coding standards etc are welcome.

class Say{
      static String[] print= {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninty", "hundred"};
      public static void main(String... args){
            try{
                  int i = Integer.parseInt(args[0]);
                  if(i >= 0 && i < 21)
                  System.out.println(print[i]);
                  else{
                        int length = args[0].length();
                        char[] arr= args[0].toCharArray();
                        if(length == 2){
                              //int i = Integer.parseInt(args[0].charAt(0));
                              switch(arr[0]){
                                    case 2:
                                          System.out.print(print[20]);
                                          break;
                                    case 3:
                                          System.out.print(print[21]);
                                          break;
                                    case 4:
                                          System.out.print(print[22]);
                                          break;
                                    case 5:
                                          System.out.print(print[23]);
                                          break;
                                    case 6:

                                          System.out.print(print[24]);
                                          break;
                                    case 7:
                                          System.out.print(print[25]);
                                          break;
                                    case 8:
                                          System.out.print(print[26]);
                                          break;
                                    case 9:
                                          System.out.print(print[27]);
                                          break;
                                    }
                                 System.out.print(print[(int)arr[1]]);
                                                                           
                        }
}
                  
            }catch(NumberFormatException e){
                  System.out.println("Please print only digits");
            }catch(ArrayIndexOutOfBoundsException e){
                  System.out.println("Print only valid numbers");
            }
      }
}
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Expert Comment

by:a_b
ID: 24782755
What is the purpose of the program?
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Author Comment

by:SunScreenCert
ID: 24782969
It takes input as numbers ranging from 0- 100 and return them in words
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Expert Comment

by:a_b
ID: 24783099
Try this out -

 
public class Test
{
    
 
    public static void main (String... args)
    {
        String[] print = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen",
                "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen", "twenty", "thirty", "forty", "fifty", "sixty", "seventy",
                "eighty", "ninty", "hundred"};
 
        try
        {
            String str = "45";
            int i = Integer.parseInt(str);
            if (i >= 0 && i < 21)
                System.out.println(print[i]);
            else
            {
                int length = str.length();
                char[] arr = str.toCharArray();
                if (i < 21)
                    System.out.println(print[arr[0]]);
                else
                {
                    int a = arr[0]-48+18; 
                    int b = arr[1]-48; 
                    System.out.println(print[a]+" "+print[b]);
 
                }
           }
 
        }
        catch (NumberFormatException e)
        {
            System.out.println("Please print only digits");
        }
        catch (ArrayIndexOutOfBoundsException e)
        {
            System.out.println("Print only valid numbers");
            e.printStackTrace();
        }
    }
}

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