CODEWITHSUNDEEP
javaarraysbinary-search
Sanskar B.C.
Sanskar B.C.

Reputation: 41

Find first occurrence of an integer in a sorted list with duplicates

This code prints the first occurence of element 'k' in the array properly but the question I'm doing wants me to print -1 if the element 'k' is entirely not present in the array. I know its easy but I'm just stuck and its frustatiting any help?

n = sc.nextInt();
k = sc.nextInt();
int arr[] = new int[n];
for(int i=0;i<n;i++) {
    arr[i] = sc.nextInt();
}
for(int i=0;i<n;i++) {
    if(arr[i]==k) {
        System.out.println(i);
        break;
    }
}

Upvotes: 0

Views: 1543

Answers (3)

Joop Eggen
Joop Eggen

Reputation: 109547

Use Arrays#binarySearch:

int firstIndexOf(int[] sortedArray, int x) {
    int p = Arrays.binarySearch(sortedArray, x);
    if (p < 0) {
        return -1;
    }
    while (p > 0 && sortedArray[p - 1] == x) {
        --p;
    }
    return p;
}

Binary search splits the searched range in half repetively looking in which half to continue. It returns either the found position or the complement (~p) of the insert position.

Upvotes: 1

Giorgi Tsiklauri
Giorgi Tsiklauri

Reputation: 11120

What you are asking in the title, and what you are asking in the post body, are two different questions; however, if we will follow your question's body, that has nothing to do with binary search, and introducing boolean flag would get you what you are asking for:

boolean notFound = true;

for(int i=0; i<n; i++) {
    if(arr[i] == k) {
        System.out.println(i);
        notFound = false;
        break;
    }
}

if(notFound) System.out.println("-1");

Upvotes: 0

user3718559
user3718559

Reputation: 16

int findOccurenceOfElemet(int[] a, int k) {
        if(a.length == 0) {
            return -1;
        }

        for(int i = 0; i < a.length; i++) {
            if(a[i] == k) {
                return i;
            }
        }
        
        //return -1 if element not found
        return -1;
    }

Upvotes: 0

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