CODEWITHSUNDEEP
javaarraysdetect
Josh Susa
Josh Susa

Reputation: 173

How do I detect if a value doesn't exist in an array

Let's say I have an array N with n values. Let's also say I have another array A with n-1 values. How would I detect which value does not exist in array A. My Java code currently has two nested for loops

for(int j = 0; j < array.length; j++){
for(int k = j; k < n.length; k++){

These search through each value in each array and compares them. So how would I detect if a value that exists in array N does not exist in array A?

P.S It's been awhile since I've used Java so please let me know if there's a better way to search through two arrays.

Upvotes: 0

Views: 3436

Answers (4)

Lucas Ross
Lucas Ross

Reputation: 1089

int[] n = new int[] {1,2,3,4};
int[] a = new int[] {2,3,4};

Set<Integer> aSet = new HashSet<>();
for (int i = 0; i < a.length; i++) {
    aSet.add(a[i]);
}

Set<Integer> valuesNotInA = new HashSet<>();
for (int i = 0; i < n.length; i++) {
    if (aSet.add(n[i])) {
        valuesNotInA.add(n[i]);
    }
}

Upvotes: 0

Afsin Buyuksarac
Afsin Buyuksarac

Reputation: 298

Simply you should check the array of bigger size elements exists in the other one. 

int i = 0; // start a global "i" for marking Array N
for(i = 0; i < N.length; i++){

   int k = 0; // start a local-global k for marking Array A. 
   for(k = 0; k < A.length; k++){
      if (A[k] == N[i]) {
         break;
      }
   }

   // if k reaches to end of the array A then we found the missing num
   if (k==A.length) {
      break;
   }
}

// Still in any case of giving wrong inputs. if i reaches to the end of the Array N then no missing values found. 
if (i != N.length) 
    System.out.println("the number missing is : " + N[i]);

Upvotes: 0

Akash Thakare
Akash Thakare

Reputation: 22972

You can achieve this easily with List,

List<Integer> xList =  Arrays.asList(new Integer[]{1,2,3,4});
List<Integer> yList =  Arrays.asList(new Integer[]{1,2,3});
List<Integer> missingList =  new ArrayList<Integer>(xList);
missingList.removeAll(yList);
System.out.println("Elements are in x but not in y are : "+missingList);

OUTPUT

Elements are in x but not in y are : [4]

Upvotes: 1

mvd
mvd

Reputation: 2720

You could use a library like Guava to get the difference of two sets, then see which elements are only present in A, or which elements are only present in N.

Upvotes: 0

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