添加 problem 61

Algorithms/61.Rotate List/README.md

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+# [61. Rotate List](https://leetcode.com/problems/rotate-list/description/)
+
+## 题目
+
+Given a linked list, rotate the list to the right by k places, where k is non-negative.
+
+Example 1:  
+
+```
+Input: 1->2->3->4->5->NULL, k = 2
+Output: 4->5->1->2->3->NULL
+Explanation:
+rotate 1 steps to the right: 5->1->2->3->4->NULL
+rotate 2 steps to the right: 4->5->1->2->3->NULL 
+```
+
+Example 2:  
+
+```
+Input: 0->1->2->NULL, k = 4
+Output: 2->0->1->NULL
+Explanation:
+rotate 1 steps to the right: 2->0->1->NULL
+rotate 2 steps to the right: 1->2->0->NULL
+rotate 3 steps to the right: 0->1->2->NULL
+rotate 4 steps to the right: 2->0->1->NULL 
+```
+
+## 题目大意
+
+旋转链表 K 次。
+
+这道题需要注意的点是，K 可能很大，K = 2000000000 ，如果是循环肯定会超时。应该找出 O(n) 的复杂度的算法才行。由于是循环旋转，最终状态其实是确定的，利用链表的长度取余可以得到链表的最终旋转结果。

Algorithms/61.Rotate List/Rotate List.go

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+package leetcode
+
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+func rotateRight(head *ListNode, k int) *ListNode {
+	if head == nil || head.Next == nil || k == 0 {
+		return head
+	}
+	newHead := &ListNode{Val: 0, Next: head}
+	len := 0
+	cur := newHead
+	for cur.Next != nil {
+		len++
+		cur = cur.Next
+	}
+	if (k % len) == 0 {
+		return head
+	}
+	cur.Next = head
+	cur = newHead
+	for i := len - k%len; i > 0; i-- {
+		cur = cur.Next
+	}
+	res := &ListNode{Val: 0, Next: cur.Next}
+	cur.Next = nil
+	return res.Next
+}

Algorithms/61.Rotate List/Rotate List_test.go

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+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question61 struct {
+	para61
+	ans61
+}
+
+// para 是参数
+// one 代表第一个参数
+type para61 struct {
+	one []int
+	k   int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans61 struct {
+	one []int
+}
+
+func Test_Problem61(t *testing.T) {
+
+	qs := []question61{
+
+		question61{
+			para61{[]int{1, 2, 3, 4, 5}, 2},
+			ans61{[]int{4, 5, 1, 2, 3}},
+		},
+
+		question61{
+			para61{[]int{1, 2, 3, 4, 5}, 3},
+			ans61{[]int{4, 5, 1, 2, 3}},
+		},
+
+		question61{
+			para61{[]int{0, 1, 2}, 4},
+			ans61{[]int{2, 0, 1}},
+		},
+
+		question61{
+			para61{[]int{1, 1, 1, 2}, 3},
+			ans61{[]int{1, 1, 2, 1}},
+		},
+
+		question61{
+			para61{[]int{1}, 10},
+			ans61{[]int{1}},
+		},
+
+		question61{
+			para61{[]int{}, 100},
+			ans61{[]int{}},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 61------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans61, q.para61
+		fmt.Printf("【input】:%v       【output】:%v\n", p, L2s(rotateRight(S2l(p.one), p.k)))
+	}
+	fmt.Printf("\n\n\n")
+}