牛客网-BM2 链表内指定区间反转

用到了BM1的思路。

 

#include <stdio.h>


struct ListNode {
int val;
struct ListNode *next;
};

struct ListNode* reverseBetween(struct ListNode* head, int m, int n ) {
    if (head == NULL) return NULL;
    if (m == n) return head;
    
    struct ListNode* start = head;
    struct ListNode* startPre;
    struct ListNode* p = head;
    
    // 先到m的位置
    int pos = 1;
    while(pos < m) {
        startPre = p;
        p = p->next;
        start = p;
        pos++;
    }
    
    struct ListNode* end = start;
    p = end->next;
    //printf("sss %d %d\n", start->val, p->val);
    // 把p放在最前面，实现倒序 
    // 1.end的next指向p的next 
    // 2.把head放到p之后
    while(pos < n) {
        end->next = p->next;
        p->next = start;
        
        start = p;
        p = end->next;
        pos++;
    }
    // 追加逆序数据 
    if (m != 1) {
        startPre->next = start;
    } else {
        head = start;
    }
    
    return head;
}

void printListNode(struct ListNode* pHead) {
    struct ListNode *p = pHead;
    while(p != NULL) {
        printf("%d ", p->val);
        p = p->next;
    }
    printf("\n");
}

int main() {
    
    ListNode pHead;
    pHead.val = 3;
    ListNode node2;
    node2.val = 5;
    node2.next = NULL;
    
    pHead.next = &node2;
    printListNode(&pHead);
     
    struct ListNode *head = reverseBetween(&pHead, 1, 2);
    printListNode(head);
    
    return 0;
}