19. Remove Nth Node From End of List

Author: kimi0230

Leetcode/0019.Remove-Nth-Node-From-End-of-List/README.md

@@ -0,0 +1,79 @@
+# [19. Remove Nth Node From End of List](https://leetcode.com/problems/middle-of-the-linked-list/)
+###### tags: `Medium` `Leetcode` `two pointers`
+
+## 題目
+Given the head of a linked list, remove the nth node from the end of the list and return its head.
+
+Example 1:
+![](https://assets.leetcode.com/uploads/2020/10/03/remove_ex1.jpg)
+```
+Input: head = [1,2,3,4,5], n = 2
+Output: [1,2,3,5]
+```
+
+Example 2:
+```
+Input: head = [1], n = 1
+Output: []
+```
+
+Example 3:
+```
+Input: head = [1,2], n = 1
+Output: [1]
+```
+
+Constraints:
+* The number of nodes in the list is sz.
+* 1 <= sz <= 30
+* 0 <= Node.val <= 100
+* 1 <= n <= sz
+
+
+## 題目大意
+找尋單linked list的 倒數第 n 個元素並刪除.
+返回該 linked list的頭節點
+
+## 解題思路
+先讓 fast走 `k` 步, 然後 `fast slow 同速前進`
+這樣當fast走到nil時, slow所在位置就是在倒數第 k 的節點
+
+## 來源
+* https://leetcode.com/problems/remove-nth-node-from-end-of-list/
+
+## 解答
+https://github.com/kimi0230/LeetcodeGolang/blob/master/Leetcode/0019.Remove-Nth-Node-From-End-of-List/main.go
+
+```go
+package removenthnodefromendoflist
+
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+func RemoveNthFromEnd(head *ListNode, n int) *ListNode {
+	dummyHead := &ListNode{Next: head}
+	preSlow, slow, fast := dummyHead, head, head
+	for fast != nil {
+		if n <= 0 {
+			// 先讓 fast走 `k` 步, 然後 `fast slow 同速前進`
+			// 這樣當fast走到nil時, slow所在位置就是在倒數第 k 的節點
+			preSlow = slow
+			slow = slow.Next
+		}
+		n--
+		fast = fast.Next
+	}
+	preSlow.Next = slow.Next
+	return dummyHead.Next
+}
+```

Leetcode/0019.Remove-Nth-Node-From-End-of-List/main.go

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+package removenthnodefromendoflist
+
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+func RemoveNthFromEnd(head *ListNode, n int) *ListNode {
+	dummyHead := &ListNode{Next: head}
+	preSlow, slow, fast := dummyHead, head, head
+	for fast != nil {
+		if n <= 0 {
+			// 先讓 fast走 `k` 步, 然後 `fast slow 同速前進`
+			// 這樣當fast走到nil時, slow所在位置就是在倒數第 k 的節點
+			preSlow = slow
+			slow = slow.Next
+		}
+		n--
+		fast = fast.Next
+	}
+	preSlow.Next = slow.Next
+	return dummyHead.Next
+}

Leetcode/0019.Remove-Nth-Node-From-End-of-List/main_test.go

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+package removenthnodefromendoflist
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestRemoveNthFromEnd(t *testing.T) {
+	a := &ListNode{1, nil}
+	b := &ListNode{2, nil}
+	c := &ListNode{3, nil}
+	d := &ListNode{4, nil}
+	e := &ListNode{5, nil}
+
+	a.Next = b
+	b.Next = c
+	c.Next = d
+	d.Next = e
+	e.Next = nil
+
+	tests := []struct {
+		arg1 *ListNode
+		arg2 int
+		want []int
+	}{
+		{
+			arg1: a,
+			arg2: 2,
+			want: []int{1, 2, 3, 5},
+		},
+	}
+
+	for _, tt := range tests {
+		got := RemoveNthFromEnd(tt.arg1, tt.arg2)
+
+		gotArr := []int{}
+		for got != nil {
+			gotArr = append(gotArr, got.Val)
+			got = got.Next
+		}
+		if !reflect.DeepEqual(gotArr, tt.want) {
+			t.Errorf("got = %v, want = %v", gotArr, tt.want)
+		}
+	}
+}

README.md

@@ -47,6 +47,7 @@
 
 | No. | Title | Solution | Difficulty | Time | Space | Topic |
 |-----|:-----:|:--------:|------------|------|-------|-------|
+| 0019 | [Remove Nth Node From End of List](https://leetcode.com/problems/middle-of-the-linked-list/) | [Go](https://github.com/kimi0230/LeetcodeGolang/tree/master/Leetcode/0019.Remove-Nth-Node-From-End-of-List) | Medium | O(n) | O(1) | Linked List, Two Pointers |
 | 0141 | [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle) | [Go](https://github.com/kimi0230/LeetcodeGolang/tree/master/Leetcode/0141.Linked-List-Cycle) | Easy | O(n) | O(1) | Linked List, Two Pointers |
 | 0142 | [Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii/) | [Go](https://github.com/kimi0230/LeetcodeGolang/tree/master/Leetcode/0142.Linked-List-CycleII) | Medium | O(n) | O(1) | Linked List, Two Pointers |
 | 0876 | [Middle of the Linked List](https://leetcode.com/problems/middle-of-the-linked-list/) | [Go](https://github.com/kimi0230/LeetcodeGolang/tree/master/Leetcode/0876.Middle-of-the-Linked-List) | Easy |  |  | Linked List, Two Pointers |
@@ -137,6 +138,7 @@ https://labuladong.gitee.io/algo/2/20/56/
 
 | No. | Title | Solution | Difficulty | Time | Space | Topic |
 |-----|:-----:|:--------:|------------|------|-------|-------|
+| 0019 | [Remove Nth Node From End of List](https://leetcode.com/problems/middle-of-the-linked-list/) | [Go](https://github.com/kimi0230/LeetcodeGolang/tree/master/Leetcode/0019.Remove-Nth-Node-From-End-of-List) | Medium | O(n) | O(1) | Linked List, Two Pointers |
 | 0141 | [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle) | [Go](https://github.com/kimi0230/LeetcodeGolang/tree/master/Leetcode/0141.Linked-List-Cycle) | Easy | O(n) | O(1) | Linked List, Two Pointers |
 | 0142 | [Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii/) | [Go](https://github.com/kimi0230/LeetcodeGolang/tree/master/Leetcode/0142.Linked-List-CycleII) | Medium | O(n) | O(1) | Linked List, Two Pointers |
 | 0344 | [Reverse String](https://leetcode.com/problems/reverse-string/) | [Go](https://github.com/kimi0230/LeetcodeGolang/tree/master/Leetcode/0344.Reverse-String) | Easy | O(n) |  O(1) | Two Pointers |