> For the complete documentation index, see [llms.txt](https://nitinranganath.gitbook.io/data-structures/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://nitinranganath.gitbook.io/data-structures/arrays/duplicates-in-an-array.md).

# Duplicates in an Array

### Finding Duplicates in a Sorted Array:

```c
void findDuplicates(int a[], int n) {

    int lastDuplicate = 0;
    printf("Duplicates in the array :\n");

    for (int i = 0; i < n; i++) {
        // If two or more same elements appear consecutively
        if (a[i] == a[i+1] && lastDuplicate != a[i]) {
            printf("%d\t", a[i]);
            // Keeping track of latest duplicate to avoid
            // printing the same duplicate again
            lastDuplicate = a[i];
        }
    }
    printf("\n");
    
}
```

### Counting Duplicates in a Sorted Array:

```c
void countDuplicates(int a[], int n) {

    int j;
    printf("Duplicates in the array :\n");

    for (int i = 0; i < n-1; i++) {
        if (a[i] == a[i+1]) {
            // Start counting duplicates from i + 1
            j = i + 1;
            while (a[i] == a[j]) {
                // Finding the number of duplicates
                j++;
            }
            printf("%d is appearing %d times\n", a[i], j-i);
            // Start looking for duplicates again
            i = j - 1; 
        }    
    }

}
```

### Using Hash Array:

```c
void findAndCountDuplicates(int a[], int n, int high) {

    // Creating a hash array and initializing with 0
    // Size of hash array = maximum element in input array
    int h[high];
    for (int i = 0; i < high; i++) {
        h[i] = 0;
    }
    
    // Incrementing hash table values as per the numbers in
    // original input array
    for (int i = 0; i < n; i++) {
        h[a[i]]++;
    }
    
    // If any element in hash table has value > 1,
    // it means that the element is repeated
    for (int i = 0; i <= high; i++) {
        if (h[i] > 1) {
            printf("%d appears %d times\n", i, h[i]);
        }
    }

}
```

Contributed by Nitin Ranganath


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://nitinranganath.gitbook.io/data-structures/arrays/duplicates-in-an-array.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.