Saving memory and CPU in java loops

Question

this (obvious) code i've writen works well, but for testing purposes, i should make it work for a "one million" sized array in a reasonable time by saving CPU Cycles and saving as much memory as i can.
any suggestions please?
!!! the array is arranged in ascending order !!!

import java.util.Arrays;

class A {
static boolean exists(int[] ints, int k) {
    for(int integer : ints){
        if(integer == k){
            return true; 
        }
    }
    return false;
}

binary search if you shoud use an array, otherwise you can use hash — Santiago Salem, Jan 24 '18 at 19:59
Maybe this can help you: https://stackoverflow.com/questions/1128723/how-can-i-test-if-an-array-contains-a-certain-value — María, Jan 24 '18 at 20:00

score 2 · Accepted Answer · answered Jan 24 '18 at 19:58

2

Since your array is in ascending order, one thing you could do (i think) is to make a binary search instead of a linear search.

answered Jan 24 '18 at 19:58

George Z.

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1

`int index = Arrays.binarySearch(new int[] {1,2,4}, 2);` – Aniket Sahrawat Jan 24 '18 at 20:00

davidxxx · Answer 2 · 2018-01-24T20:07:41.073

You could use a Set<Integer> that relies on hashing rather than an array where you iterate sequentially.

static boolean exists(Set<Integer> ints, int k) {
     return ints.contains(k);
}

You could convert the array to a Set and pass it to the method as many times as required :

Set<Integer> set = Arrays.stream(ints).boxed().collect(Collectors.toSet());
boolean isExist = exists(set, 15);
 ...
isExist = exists(set, 5005);
 ...
isExist = exists(set, 355);

Saving memory and CPU in java loops

2 Answers2