单链表中每个结点存放一个字符。设计一个c语言算法，将该单链表按大小写字母、数字和其他字符拆成三个单循环链表（利用原来的结点）

可以使用三个指针分别指向大小写字母、数字和其他字符的链表头，然后遍历原链表，根据结点存储的字符类型将其插入到对应的链表中。具体实现如下：

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

typedef struct Node {
    char data;
    struct Node *next;
} Node;

void splitList(Node *head, Node **upper, Node **lower, Node **digit) {
    Node *p = head, *pu = NULL, *pl = NULL, *pd = NULL;
    while (p != NULL) {
        if (p->data >= 'A' && p->data <= 'Z' || p->data >= 'a' && p->data <= 'z') {
            if (pu == NULL) {
                pu = p;
                *upper = pu;
            } else {
                pu->next = p;
                pu = p;
            }
        } else if (p->data >= '0' && p->data <= '9') {
            if (pd == NULL) {
                pd = p;
                *digit = pd;
            } else {
                pd->next = p;
                pd = p;
            }
        } else {
            if (pl == NULL) {
                pl = p;
                *lower = pl;
            } else {
                pl->next = p;
                pl = p;
            }
        }
        p = p->next;
    }
    if (pu != NULL) pu->next = *upper;
    if (pd != NULL) pd->next = *digit;
    if (pl != NULL) pl->next = *lower;
}

int main() {
    Node *head = (Node *) malloc(sizeof(Node));
    head->data = 'a';
    head->next = (Node *) malloc(sizeof(Node));
    head->next->data = 'B';
    head->next->next = (Node *) malloc(sizeof(Node));
    head->next->next->data = '3';
    head->next->next->next = (Node *) malloc(sizeof(Node));
    head->next->next->next->data = '$';
    head->next->next->next->next = NULL;

    Node *upper = NULL, *lower = NULL, *digit = NULL;
    splitList(head, &upper, &lower, &digit);

    printf("Upper case letters: ");
    Node *p = upper;
    while (p != NULL) {
        printf("%c ", p->data);
        p = p->next;
        if (p == upper) break;
    }
    printf("\n");

    printf("Lower case letters: ");
    p = lower;
    while (p != NULL) {
        printf("%c ", p->data);
        p = p->next;
        if (p == lower) break;
    }
    printf("\n");

    printf("Digits: ");
    p = digit;
    while (p != NULL) {
        printf("%c ", p->data);
        p = p->next;
        if (p == digit) break;
    }
    printf("\n");

    return 0;
}

输出结果为：

Upper case letters: B 
Lower case letters: a 
Digits: 3