206 reverse linked list

两种方法 一种迭代 一种递归 都需要熟练掌握

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* reverseList(struct ListNode* head) {
    if(head == NULL)
        return NULL;
    if(head->next == NULL)
        return head;
    struct ListNode *node;

    node = reverseList(head->next);
    head->next->next = head;
    head->next = NULL;

    return node;    
}

struct ListNode* reverseList(struct ListNode* head) {
    if(head == NULL || head->next == NULL)
        return head;
    struct ListNode *prev, *curr, *next;
    curr = head;
    prev = NULL;
    next = NULL;
    while(curr){
        next = curr->next;
        curr->next = prev;
        prev = curr;
        curr = next;
    }

    return prev;    
}