Question

Write a c program using a recursive solution that reads a single positive integer, N, and prints out all possible distinct lists that include each positive integer from 1 to N. So, for example, if N is three, your output should be the following 6 lines:
1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1

Answer 1

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void print_list(int N, int* line, int lineLength, char* numbersUsed)
{
int n;
for (n = 1; n <= N; n++)
if (!numbersUsed[n - 1])
{
line[lineLength] = n;
if (lineLength + 1 == N)
{
int k;
for (k = 0; k < N; k++)
printf("%5d", line[k]);
putchar('\n');
}
else
{
numbersUsed[n - 1] = 1;
print_list(N, line, lineLength + 1, numbersUsed);
numbersUsed[n - 1] = 0;
}
}
}

int main()
{
int N;
int* line;
char* numbersUsed;

printf("Enter N: ");
scanf("%d", &N);

line = (int*)malloc(N * sizeof(int));
numbersUsed = (char*)malloc(N * sizeof(char));

memset(numbersUsed, 0, N * sizeof(char));
print_list(N, line, 0, numbersUsed);

free(numbersUsed);
free(line);
return 0;
}