C实现生成n个元素的全排列

// =====================【全排列】==================

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

#define NUM 4
char arr[NUM] = { 0 };

int m_solution_num = 0;

void init()
{
    for (int i = 0; i != NUM; i++)
    {
        arr[i] = 'A' + i;
    }
}

void output()
{
    printf("第%d组解为：n",++m_solution_num);
    for (int i = 0; i != NUM; i++)
    {
        printf("%ct",arr[i]);
    }
    printf("n");
}

void swap(char * a,char * b)
{
    char aa = *a;
    char bb = *b;

    aa = aa ^ bb;
    bb = aa ^ bb;
    aa = aa ^ bb;

    *a = aa;
    *b = bb;
}

void solve(int curpos)
{
    if (curpos >= NUM)
    {
        output();
        return;
    }

    // 原来写的是0， 这里应该是curpos
    for (int i = curpos; i != NUM; i++)
    {
        swap(&arr[curpos],&arr[i]);
        solve(++i);
        --i;
        swap(&arr[curpos],&arr[i]);

    }
}

void main()
{
    init();
    solve(0);
}