一道百度机器学习工程师职位的面试题

char a, b, c;
for(a = 'a'; a<='z'; a++)
    for(b= a+1; b<='z'; b++)
        for(c = b+1; c<='z'; c++)
            printf("%c%c%c\n", a, b, c);

#include <stdio.h>
//某个数二进制位上有几个 1
int bit(unsigned int x)
{
    int c = 0;
    while( x )
    {
        c++;
        x = (x & (x - 1));
    }
    return c;
}

void print(unsigned int x, int count)
{
    int i = 0;
    //控制，假如count为3， x 里边有三个 1
    if( bit(x) == count )
    {
        for(i=0; i<26; i++)
        {
            if( x & 1)
            {
                printf("%c ", (char)('a' + i));
            }
            x = (x >> 1);
        }
        printf("\n");
    }
}
int main()
{
    const unsigned int N = 26;
    const unsigned int C = 3;
    const unsigned int X = (1 << N) - 1;  //X=(1<<26)-1
    unsigned int i = 0;
    
    for(i=0; i<X; i++)
    {
        print(i, C);
    }
    return 0;
}