/
reverse-linked-list.cpp
52 lines (47 loc) · 1 KB
/
reverse-linked-list.cpp
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// Reverse a singly linked list.
//
// Example:
//
//
// Input: 1->2->3->4->5->NULL
// Output: 5->4->3->2->1->NULL
//
//
// Follow up:
//
// A linked list can be reversed either iteratively or recursively. Could you implement both?
//
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
private:
ListNode* helper(ListNode *parent, ListNode* node) {
ListNode* newParent;
if (node != NULL) {
newParent = node->next;
node->next = parent;
if (newParent != NULL) {
newParent = helper(node, newParent);
}
}
else {
newParent = NULL;
}
if (newParent != NULL) {
return newParent;
}
else {
return node;
}
}
public:
ListNode* reverseList(ListNode* head) {
return helper(NULL, head);
}
};