/* 华科机试练手
 * 回溯法解决 排列组合问题
 * 1 : 全排列
 * 2 ：可重复全排列
 * 3 : 不可重复的选择排序
 * ……
 */
#include <stdlib.h>
#include <stdio.h>
int solution[100];

/* 可重复全排 */
int Perm(int a[], int n, int level)
{
    int i;
    static int sum = 0;
    if(level == n)
    {
        sum++;
        for(i=0; i<level; i++)
            printf("%d\t",solution[i]);
        printf("\n");
        return;
    }
    for(i=0; i<n; i++)
    {
        if(1)
        {
            solution[level] = a[i];
            Perm(a,n,level+1);
        }
    }
    return sum;
}
/* 不可重复全排 */
int NoReptPerm(int a[], int n, int level)
{
    int i,j,selected = 0;
    static int sum = 0;
    if(level == n)
    {
        sum++;
        for(i=0; i<level; i++)
            printf("%d\t",solution[i]);
        printf("\n");
        return;
    }
    for(i=0; i<n; i++)
    {
        selected = 0;
        for(j=0; j<level; j++)//检查是否已经被选过
        {
            if(solution[j] == a[i])
            {
                selected = 1;
                break;
            }
        }
        if(!selected)//没被选过
        {
            solution[level] = a[i];//加入解向量
            NoReptPerm(a,n,level+1);
        }
    }
    return sum;
}
/* 选择排序(不可重复) */
int SelectPerm(int a[], int n, int m, int level)
{
    int i,j,selected = 0;
    static int sum = 0;
    if(level == m)
    {
        sum++;
        for(i=0; i<level; i++)
            printf("%d\t",solution[i]);
        printf("\n");
        return;
    }
    for(i=0; i<n; i++)
    {
        selected = 0;
        for(j=0; j<level; j++)//检查是否已经被选过
        {
            if(solution[j] == a[i])
            {
                selected = 1;
                break;
            }
        }
        if(!selected)//没被选过
        {
            solution[level] = a[i];//加入解向量
            SelectPerm(a,n,m,level+1);
        }
    }
    return sum;
}
int main(int argc, char *argv[])
{
    int i;
    int a[] = {1,2,3};
    i = Perm(a,3,0);
    printf("Total : %d\n",i);
    i = NoReptPerm(a,3,0);
    printf("Total : %d\n",i);
    i = SelectPerm(a,3,2,0);
    printf("Total : %d\n",i);
    return 1;
}