closest_k_values.cpp

#include<stdio.h>

/* Function to find the cross over point (the point before
which elements are smaller than or equal to x and after
which greater than x)*/
int findCrossOver(int arr[], int low, int high, int x)
{
// Base cases
if (arr[high] <= x) // x is greater than all
	return high;
if (arr[low] > x) // x is smaller than all
	return low;

// Find the middle point
int mid = (low + high)/2; /* low + (high - low)/2 */

/* If x is same as middle element, then return mid */
if (arr[mid] <= x && arr[mid+1] > x)
	return mid;

/* If x is greater than arr[mid], then either arr[mid + 1]
	is ceiling of x or ceiling lies in arr[mid+1...high] */
if(arr[mid] < x)
	return findCrossOver(arr, mid+1, high, x);

return findCrossOver(arr, low, mid - 1, x);
}

// This function prints k closest elements to x in arr[].
// n is the number of elements in arr[]
void printKclosest(int arr[], int x, int k, int n)
{
	// Find the crossover point
	int l = findCrossOver(arr, 0, n-1, x);
	int r = l+1; // Right index to search
	int count = 0; // To keep track of count of elements already printed

	// If x is present in arr[], then reduce left index
	// Assumption: all elements in arr[] are distinct
	if (arr[l] == x) l--;

	// Compare elements on left and right of crossover
	// point to find the k closest elements
	while (l >= 0 && r < n && count < k)
	{
		if (x - arr[l] < arr[r] - x)
			printf("%d ", arr[l--]);
		else
			printf("%d ", arr[r++]);
		count++;
	}

	// If there are no more elements on right side, then
	// print left elements
	while (count < k && l >= 0)
		printf("%d ", arr[l--]), count++;

	// If there are no more elements on left side, then
	// print right elements
	while (count < k && r < n)
		printf("%d ", arr[r++]), count++;
}

/* Driver program to check above functions */
int main()
{
int arr[] ={12, 16, 22, 30, 35, 39, 42,
			45, 48, 50, 53, 55, 56};
int n = sizeof(arr)/sizeof(arr[0]);
int x = 35, k = 4;
printKclosest(arr, x, 4, n);
return 0;
}