题解 | #链表内指定区间反转#

/**
 * 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 m int整型
 * @param n int整型
 * @return ListNode类
 */
struct ListNode* reverseBetween(struct ListNode* head, int m, int n ) {
    // write code here
    if (head == NULL || head->next == NULL || m == n) {
        return head;
    }

    struct ListNode* phead = head;
    struct ListNode* pend = head;
    struct ListNode* pphead = NULL;

    for (int i = 0; i < m - 1; i++) {
        pphead = phead;
        phead = phead -> next;
    }
    for (int i = 0; i < n - 1; i++) {
        pend = pend -> next;
    }

    struct ListNode* next = NULL;
    struct ListNode* prev = pend -> next;
    struct ListNode* curr = phead;
    pend -> next = NULL;

    while (curr != NULL) {
        next = curr -> next;
        curr -> next = prev;
        prev = curr;
        curr = next;
    }

    if(pphead != NULL){
        pphead -> next = pend;
    }else{
        head = pend;
    }


    return head;
}