CountPairsWithSum

package Udemyprograms;

public class Arrays15GeeksForGeeks {

  public static int CountPairsWithGivenSum(int[] arr, int sum) {
    /**
     * intialise two pointers front = 0;rear = 0;
     * intialise the count = 0;
     * iterate a loop
     * check whether the sum of the frontElemet and rearElement is meeting the target
     * if s increase the count
     * check whether the rear is equal to front 
     * if s make front++
     * rear = arr.length
     */
    int count = 0;
    int front = 0, rear = arr.length - 1;
    while (front < arr.length - 1) {
      if (arr[front] + arr[rear] == sum) {
        count++;
      }
      rear--;
      if (front == rear) {
        front++;
        rear = arr.length - 1;
      }
    }
    return count;
  }

  public static void main(String args[]) {
    int[] arr = {10, 12, 10, 15, -1, 7, 6,
      5, 4, 2, 1, 1, 1};
    System.out.println(CountPairsWithGivenSum(arr, 11));
  }

}