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Algorithms for Coding Interviews in Java

Solution: Count Element Occurrence

Explore different algorithmic solutions for counting the occurrences of an element in an array. Learn the brute force approach with linear search, a binary search method that counts contiguous duplicates, and a modified binary search to find first and last occurrence indices. Understand the time complexities and trade-offs of each solution in the context of sorting and searching techniques using Java.

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Solution #1: Brute force with linear search

Java
class Count {
 public static int calcFreq(int arr[], int key) {
  int count = 0;
  //traversing the array
  for (int i = 0; i < arr.length; i++) {
   //checking if current index value matches key
   if (arr[i] == key)
    //incrementing count if it does
    count++;
  }
  return count;
 }
 public static void main(String args[]) {
  int arr[] = {-5,-3,0,1,3,3,3,3,4,5};
  int key = 3;
  System.out.println("The key \"" + key + "\" occurs " + calcFreq(arr, key) + " times in the Array.");
 }
}

This is an extremely simple way to solve this problem. We simply initialize a variable, count, to keep count and set it to 0 (line 3). We then iterate over the array (line 5), increasing count by one every time the key (value to search) is encountered ( ...