题解 | #牛群的重新分组#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 * 
 * @param head ListNode类 
 * @param k int整型 
 * @return ListNode类
 */
struct ListNode* reverseKGroup(struct ListNode* head, int k) {
    if (!head || k <= 1) {
        return head;
    }

    int length = 0;
    struct ListNode* node = head;
    while (node) {
        length++;
        node = node->next;
    }

    struct ListNode* dummy = (struct ListNode*)malloc(sizeof(struct ListNode));
    dummy->next = head;
    struct ListNode* prev = dummy;
    struct ListNode* curr = head;

    for (int i = 0; i < length / k; i++) {
        for (int j = 1; j < k; j++) {
            struct ListNode* next = curr->next;
            curr->next = next->next;
            next->next = prev->next;
            prev->next = next;
        }
        prev = curr;
        curr = curr->next;
    }

    struct ListNode* result = dummy->next;
    free(dummy);
    return result;
}