Combination

cobination.cpp

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

//排列，用的是非递归方法，即2进制方法
char letter[] = "abcdefg";

int main()
{
	int number = 1<<7;
        int index, cur;
	for (int i=1; i<number; ++i)
	{
		char tmp[] ="";
		index = 0;
		cur = i;
		while (cur)
		{
			if (cur&1)
			{
				strncat(tmp, &letter[index], 1);
			}
			index++;
			cur = cur>>1;
		}
		printf("%s\n", tmp);
	}
	return 0;
}

//usage:
//char letter[] = "abc";
//Arrange(letter, letter);
void Arrange(char *str, char *start)
{
    if (!*start)
    {
        printf("%s\n", str);
        return;
    }
    for (char *i=start; (*i)!='\0'; i++)  //基本思想是
    {
        char tmp = *start;
        *start = *i;
        *i = tmp;
        Arrange(str, start+1);
        tmp = *start;
        *start = *i;
        *i = tmp;
    }
}

void Arrange(char *str)
{
    Arrange(str, str);
}