Add Solution for 061 Rotate List

cpp/061_Rotate_List.cpp

@@ -0,0 +1,105 @@
+// 61. Rotate List
+/**
+ * Given a list, rotate the list to the right by k places, where k is non-negative.
+ * 
+ * For example:
+ * Given 1->2->3->4->5->NULL and k = 2,
+ * return 4->5->1->2->3->NULL.
+ * 
+ * Tags: Linked List, Two Pointers
+ * 
+ * Similar Problems: (E) Rotate Array
+ * 
+ * Author: Kuang Qin
+ */
+
+#include <iostream>
+
+using namespace std;
+
+/**
+ * Definition for singly-linked list.
+ */
+struct ListNode {
+    int val;
+    ListNode *next;
+    ListNode(int x) : val(x), next(NULL) {}
+    ListNode(int x, ListNode *p) : val(x), next(p) {}
+};
+
+// circle list
+class Solution_CircleList {
+public:
+    ListNode* rotateRight(ListNode* head, int k) {
+        if (head == NULL || head->next == NULL || k == 0) {
+            return head;
+        }
+        int len = 1;
+        ListNode *tail = head;
+
+        // find the end of the list
+        while (tail->next != NULL) {
+            tail = tail->next;
+            len++;
+        }
+
+        // for a cirle
+        tail->next = head;
+
+        // find new tail
+        // when k > len, shift right (k % len)
+        // (len - k % len) is the new tail position
+        for (int i = 0; i < len - k % len; i++) {
+            tail = tail->next;
+        }
+
+        head = tail->next;
+        tail->next = NULL;
+
+        return head;
+    }
+};
+
+// two pointers
+class Solution {
+public:
+    ListNode* rotateRight(ListNode* head, int k) {
+        if (head == NULL || head->next == NULL || k == 0) {
+            return head;
+        }
+        int len = 1;
+        ListNode *fast = head, *slow = head;
+
+        // move fast pointer to the end of the list
+        while (fast->next != NULL) {
+            fast = fast->next;
+            len++;
+        }
+
+        // move slow pointer to the new tail
+        // when k > len, shift right (k % len)
+        // (len - k % len) is the new tail position
+        for (int i = 1; i < len - k % len; i++) {
+            slow = slow->next;
+        }
+
+        fast->next = head;  // connect tail to head
+        head = slow->next;  // new head
+        slow->next = NULL;  // point tail to null
+
+        return head;
+    }
+};
+
+int main() {
+    ListNode node5(5), node4(4, &node5), node3(3, &node4), node2(2, &node3), node1(1, &node2);
+    Solution sol;
+    ListNode *newhead = sol.rotateRight(&node1, 3);
+    for (ListNode *p = newhead; p != NULL; p = p->next) {
+        cout << p->val << " ";
+    }
+    cout << endl;
+    cin.get();
+
+    return 0;
+}