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C Program for Pancake sorting

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  • Last Updated : 10 Jun, 2022

Given an unsorted array, sort the given array. You are allowed to do only following operation on array.

flip(arr, i): Reverse array from 0 to i 

C




/* C program for Pancake Sorting */
#include <stdio.h>
#include <stdlib.h>
 
/* Reverses arr[0..i] */
void flip(int arr[], int i)
{
 int temp, start = 0;
 while (start < i) {
  temp = arr[start];
  arr[start] = arr[i];
  arr[i] = temp;
  start++;
  i--;
 }
}
 
/* Returns index of the maximum element in arr[0..n-1] */
int findMax(int arr[], int n)
{
 int mi, i;
 for (mi = 0, i = 0; i < n; ++i)
  if (arr[i] > arr[mi])
   mi = i;
 return mi;
}
 
// The main function that sorts given array using flip
// operations
int pancakeSort(int* arr, int n)
{
 // Start from the complete array and one by one reduce
 // current size by one
 for (int curr_size = n; curr_size > 1; --curr_size) {
  // Find index of the maximum element in
  // arr[0..curr_size-1]
  int mi = findMax(arr, curr_size);
 
  // Move the maximum element to end of current array
  // if it's not already at the end
  if (mi != curr_size - 1) {
   // To move at the end, first move maximum number
   // to beginning
   flip(arr, mi);
 
   // Now move the maximum number to end by reversing
   // current array
   flip(arr, curr_size - 1);
  }
 }
}
 
/* A utility function to print an array of size n */
void printArray(int arr[], int n)
{
 for (int i = 0; i < n; ++i)
  printf("%d ", arr[i]);
}
 
// Driver program to test above function
int main()
{
 int arr[] = { 23, 10, 20, 11, 12, 6, 7 };
 int n = sizeof(arr) / sizeof(arr[0]);
 
 pancakeSort(arr, n);
 
 puts("Sorted Array ");
 printArray(arr, n);
 
 return 0;
}

Output:

Sorted Array 
6 7 10 11 12 20 23

Time Complexity: O(n2)
Auxiliary Space: O(1)

Please refer complete article on Pancake sorting for more details!


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