题解 | 牛牛的链表交换

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

// write your code here......
struct ListNode {
    int nodeVal;
    struct ListNode * next;
};


int main() {

    int n, val, i;
    scanf("%d",&n);

    struct ListNode * pHeadNode;
    struct ListNode *p, *pLastPrev,*pLastPrevPrev,*pLast, *pTemp1, *pTemp2;

    pHeadNode = (struct ListNode *) malloc(sizeof(struct ListNode));
    if(!pHeadNode) {
        return -1;
    }

    for (i = 1; i <= n; i++) {
        scanf("%d",&val);
        p = (struct ListNode *) malloc(sizeof(struct ListNode));
        if(p) {
            p->nodeVal = val;
            p->next = NULL;
            //printf("p->nodeVal = %d", p->nodeVal);
        }

        if(i == 1) {
            pHeadNode->next = p;
            pLast = pLastPrev = p;
            pLastPrevPrev = p;
        }
        else if ( i <= 3) {
            pLast->next = p;
            pLastPrev = pLast;              
            pLast = p; 
        }
        else {
            pLast->next = p;
            pLastPrevPrev = pLastPrev;
            pLastPrev = pLast;              
            pLast = p; 
        }

    }


    if(n >= 3 && n <= 4) {
        if(pHeadNode->next != NULL && pHeadNode->next->next != NULL) {
            pTemp1 = pHeadNode->next;
            pTemp2 = pHeadNode->next->next->next;
            pHeadNode->next->next->next = pTemp1;
            pHeadNode->next = pHeadNode->next->next;
            pTemp1->next = pTemp2;
        }


        for (i = 1, p = pHeadNode->next; i <= n; i++) {
            if(i == 1) {
                pLast = pLastPrev = p;
                pLastPrevPrev = p;
            }
            else if ( i <= 3) {
                pLast->next = p;
                pLastPrev = pLast;              
                pLast = p; 
            }
            else {
                pLast->next = p;
                pLastPrevPrev = pLastPrev;
                pLastPrev = pLast;              
                pLast = p; 
            }

            p = p->next;

        }

        pLastPrevPrev->next = pLast;
        pLast->next = pLastPrev;
        pLastPrev->next = NULL;

    }
    else if (n >= 5) {
        if(pHeadNode->next != NULL && pHeadNode->next->next != NULL) {
            pTemp1 = pHeadNode->next;
            pTemp2 = pHeadNode->next->next->next;
            pHeadNode->next->next->next = pTemp1;
            pHeadNode->next = pHeadNode->next->next;
            pTemp1->next = pTemp2;
        }


        pLastPrevPrev->next = pLast;
        pLast->next = pLastPrev;
        pLastPrev->next = NULL;

    }


    p = pHeadNode->next;

    while(p != NULL) {
        printf("%d ", p->nodeVal);
        p = p->next;
    }

    // write your code here......
    

    return 0;
}