I00031 Look-and-say sequence



Look-and-say数列是一个有趣的数列。有关介绍参见维基百科的Look-and-say sequence。在OEIS网站上，数列号为A005150。

这个程序打印输出Look-and-say数列的前18项。

C语言程序如下：

/* I00031 Look-and-say sequence */

#include <stdio.h>
#include <memory.h>

#define MAXN 100000

char s[MAXN+1], t[MAXN+1];
char *ps, *pt;

int main(void)
{
    char look;
    int say, i;

    memset(s, 0, sizeof(s));
    memset(t, 0, sizeof(t));

    s[0] = '1';
    for(i=0; i<18; i++) {
        if(i & 1) {
            ps = t;
            pt = s;
        } else {
            ps = s;
            pt = t;
        }

        printf("%s
", ps);

        look = *ps;
        say = 1;
        while(*(++ps)) {
            if(*ps == look)
                say++;
            else {
                *pt++ = '0' + say;
                *pt++ = look;

                look = *ps;
                say = 1;
            }
        }
        *pt++ = '0' + say;
        *pt++ = look;
    }

    return 0;
}

运行结果如下：

1
11
21
1211
111221
312211
13112221
1113213211
31131211131221
13211311123113112211
11131221133112132113212221
3113112221232112111312211312113211
1321132132111213122112311311222113111221131221
11131221131211131231121113112221121321132132211331222113112211
311311222113111231131112132112311321322112111312211312111322212311322113212221
132113213221133112132113311211131221121321131211132221123113112221131112311332111213211322211312113211
11131221131211132221232112111312212321123113112221121113122113111231133221121321132132211331121321231231121113122113322113111221131221
31131122211311123113321112131221123113112211121312211213211321322112311311222113311213212322211211131221131211132221232112111312111213111213211231131122212322211331222113112211