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finding the min and max values in an array

Posted on 2003-02-23
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Last Modified: 2010-03-31
Could anybody give me an efficient algorithm for finding the min and max values in an unsorted array. Its not just one array that i have to process, but it may be about 20000 arrays. There is 1 min and the 1 max is for all the arrays together.
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Question by:surball
9 Comments
 
LVL 9

Accepted Solution

by:
yongsing earned 200 total points
ID: 8002582
Since the array is unsorted, you would have to go through every item in the array:

int min = Integer.MAX_VALUE;
int max = Integer.MIN_VALUE;
for (int i = 0; i < yourArray.length; i++) {
  min = yourArray[i] < min ? yourArray[i] : min;
  max = yourArray[i] > max ? yourArray{i] : max;
}
System.out.println("Min = " + min);
System.out.println("Max = " + max);
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LVL 2

Expert Comment

by:functionpointer
ID: 8004042
yongsing is right. you have to check every value. but if you wrap a controller type class around all your arrays could limit the amount of searching you have to do. That way you would only have to check the min/max on addition, removal(if the array contained a min or max), or alteration of the data in the underlying arrays ( which you could control in the accessor as well ).
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Expert Comment

by:swargdwar
ID: 8007260
youngsing's code is wrong!!!!!!!!!!!!!!!!!

int min = Integer.MAX_VALUE;
int max = Integer.MIN_VALUE;
for (int i = 0; i < yourArray.length; i++) {
 min = yourArray[i] < min ? yourArray[i] : min;
 max = yourArray[i] > max ? yourArray{i] : max;
}
System.out.println("Min = " + min);
System.out.println("Max = " + max);

/********************************************/
NO INTEGER WILL BE LESS THAN min(Integer.MIN_VALUE).
HE SHOULD HAVE INITIALIZED IT AS

int min = yourArray[0] ;
int max = yourArray[0] ;

/*************************************************/


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LVL 9

Expert Comment

by:yongsing
ID: 8007361
>> NO INTEGER WILL BE LESS THAN min(Integer.MIN_VALUE).

That's true. I never claim that any integer will be less than Integer.MIN_VALUE. My code still works.
0
 

Expert Comment

by:swargdwar
ID: 8007497
suppose his array contains

min value of -1000
and max value of +1000

ur code will work but it will show
max=Integer.MAX_VALUE;
min=Integer.MIN_VALUE;

not
max=1000
min=-1000

because
1000!>Integer.MAX_VALUE  //max = yourArray[i] > max ? yourArray{i] : max;

-1000!<Integer.MIN_VALUE //min = yourArray[i] < min ? yourArray[i] : min;

0
 
LVL 9

Expert Comment

by:yongsing
ID: 8013187
Well, why don't you try this:

public class TestMinMax {

  public static void main(String[] args){
    int[] yourArray = {0, -1, 345, -45, 1000, -666, -1000, 234};
    int min = Integer.MAX_VALUE;
    int max = Integer.MIN_VALUE;
    for (int i = 0; i < yourArray.length; i++) {
      min = yourArray[i] < min ? yourArray[i] : min;
      max = yourArray[i] > max ? yourArray[i] : max;
    }
    System.out.println("Min = " + min);
    System.out.println("Max = " + max);
  }
}

It prints:

Min = -1000
Max = 1000

Perhaps you're convinced now.
0
 

Author Comment

by:surball
ID: 8013213
The answer that yongsing has given (and i accepted it as the answer) works fine
0
 

Expert Comment

by:swargdwar
ID: 8014213
hi youngsing
i am sorry man!
ur code works because

int min = Integer.MAX_VALUE;//here min is equal to MAX
int max = Integer.MIN_VALUE;//here max is equal to MIN

i did not notice this swapping nor did u point this out in
ur comments.
i regret it.
regards
swargdwar

0
 
LVL 9

Expert Comment

by:yongsing
ID: 8014279
No problem, swargdwar. :) In fact, initializing the min and max variables to the first element of the array might be a better idea, because it's not that confusing.
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