generate stack perm

stackper.c

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

#define MAX 100

void generate(int input[], int n, int in,
              int stack[], int top,
              int output[], int out) {
	//if input and stack empty we reached base case
    if (in == n && top == -1) {
        for (int i = 0; i < out; i++) {
            printf("%d ", output[i]);
        }
        printf("\n");
        return;
    }

    // either we can push from input to stack
    if (in < n) {
        stack[++top] = input[in];
        generate(input, n, in + 1, stack, top, output, out);
        top--; // backtrack
    }

    //or we can pop from stack to output
    if (top != -1) {
        int val = stack[top--];
        output[out++] = val;
        generate(input, n, in, stack, top, output, out);
        out--; // backtrack
        stack[++top] = val; // restore
    }
}

int main() {
    int n;
    printf("Enter n: ");
    scanf("%d", &n);

    int input[MAX];
	printf("Enter %d elements of the input:\n", n);
	for(int i = 0; i < n; i++) scanf("%d", &input[i]);
    int stack[MAX], output[MAX];

    printf("All possible stack permutations:\n");
    generate(input, n, 0, stack, -1, output, 0);

    return 0;
}