feat: add solutions to lcci problem: No.02.02 (#2306)

No.02.02.Kth Node From End of List

Author: yanglbme

lcci/02.02.Kth Node From End of List/README.md

@@ -20,7 +20,11 @@
 
 ## 解法
 
-### 方法一
+### 方法一：快慢指针
+
+我们定义两个指针 `slow` 和 `fast`，初始时都指向链表头节点 `head`。然后 `fast` 指针先向前移动 $k$ 步，然后 `slow` 和 `fast` 指针同时向前移动，直到 `fast` 指针指向链表末尾。此时 `slow` 指针指向的节点就是倒数第 $k$ 个节点。
+
+时间复杂度 $O(n)$，其中 $n$ 是链表的长度。空间复杂度 $O(1)$。
 
 <!-- tabs:start -->
 
@@ -38,7 +42,8 @@ class Solution:
         for _ in range(k):
             fast = fast.next
         while fast:
-            slow, fast = slow.next, fast.next
+            slow = slow.next
+            fast = fast.next
         return slow.val
 ```
 
@@ -80,7 +85,7 @@ public:
     int kthToLast(ListNode* head, int k) {
         ListNode* fast = head;
         ListNode* slow = head;
-        while (k-- > 0) {
+        while (k--) {
             fast = fast->next;
         }
         while (fast) {
@@ -93,9 +98,16 @@ public:
 ```
 
 ```go
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
 func kthToLast(head *ListNode, k int) int {
 	slow, fast := head, head
-	for i := 0; i < k; i++ {
+	for ; k > 0; k-- {
 		fast = fast.Next
 	}
 	for fast != nil {
@@ -106,6 +118,32 @@ func kthToLast(head *ListNode, k int) int {
 }
 ```
 
+```ts
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function kthToLast(head: ListNode | null, k: number): number {
+    let [slow, fast] = [head, head];
+    while (k--) {
+        fast = fast.next;
+    }
+    while (fast !== null) {
+        slow = slow.next;
+        fast = fast.next;
+    }
+    return slow.val;
+}
+```
+
 ```rust
 // Definition for singly-linked list.
 // #[derive(PartialEq, Eq, Clone, Debug)]
@@ -153,14 +191,13 @@ impl Solution {
  * @return {number}
  */
 var kthToLast = function (head, k) {
-    let fast = head,
-        slow = head;
-    for (let i = 0; i < k; i++) {
+    let [slow, fast] = [head, head];
+    while (k--) {
         fast = fast.next;
     }
-    while (fast != null) {
-        fast = fast.next;
+    while (fast !== null) {
         slow = slow.next;
+        fast = fast.next;
     }
     return slow.val;
 };

lcci/02.02.Kth Node From End of List/README_EN.md

@@ -22,7 +22,11 @@
 
 ## Solutions
 
-### Solution 1
+### Solution 1: Two Pointers
+
+We define two pointers `slow` and `fast`, both initially pointing to the head node `head`. Then the `fast` pointer moves forward $k$ steps first, and then the `slow` and `fast` pointers move forward together until the `fast` pointer points to the end of the list. At this point, the node pointed to by the `slow` pointer is the $k$-th node from the end of the list.
+
+The time complexity is $O(n)$, where $n$ is the length of the list. The space complexity is $O(1)$.
 
 <!-- tabs:start -->
 
@@ -40,7 +44,8 @@ class Solution:
         for _ in range(k):
             fast = fast.next
         while fast:
-            slow, fast = slow.next, fast.next
+            slow = slow.next
+            fast = fast.next
         return slow.val
 ```
 
@@ -82,7 +87,7 @@ public:
     int kthToLast(ListNode* head, int k) {
         ListNode* fast = head;
         ListNode* slow = head;
-        while (k-- > 0) {
+        while (k--) {
             fast = fast->next;
         }
         while (fast) {
@@ -95,9 +100,16 @@ public:
 ```
 
 ```go
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
 func kthToLast(head *ListNode, k int) int {
 	slow, fast := head, head
-	for i := 0; i < k; i++ {
+	for ; k > 0; k-- {
 		fast = fast.Next
 	}
 	for fast != nil {
@@ -108,6 +120,32 @@ func kthToLast(head *ListNode, k int) int {
 }
 ```
 
+```ts
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function kthToLast(head: ListNode | null, k: number): number {
+    let [slow, fast] = [head, head];
+    while (k--) {
+        fast = fast.next;
+    }
+    while (fast !== null) {
+        slow = slow.next;
+        fast = fast.next;
+    }
+    return slow.val;
+}
+```
+
 ```rust
 // Definition for singly-linked list.
 // #[derive(PartialEq, Eq, Clone, Debug)]
@@ -155,14 +193,13 @@ impl Solution {
  * @return {number}
  */
 var kthToLast = function (head, k) {
-    let fast = head,
-        slow = head;
-    for (let i = 0; i < k; i++) {
+    let [slow, fast] = [head, head];
+    while (k--) {
         fast = fast.next;
     }
-    while (fast != null) {
-        fast = fast.next;
+    while (fast !== null) {
         slow = slow.next;
+        fast = fast.next;
     }
     return slow.val;
 };

lcci/02.02.Kth Node From End of List/Solution.cpp

@@ -11,7 +11,7 @@ class Solution {
     int kthToLast(ListNode* head, int k) {
         ListNode* fast = head;
         ListNode* slow = head;
-        while (k-- > 0) {
+        while (k--) {
             fast = fast->next;
         }
         while (fast) {

lcci/02.02.Kth Node From End of List/Solution.go

@@ -1,6 +1,13 @@
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
 func kthToLast(head *ListNode, k int) int {
 	slow, fast := head, head
-	for i := 0; i < k; i++ {
+	for ; k > 0; k-- {
 		fast = fast.Next
 	}
 	for fast != nil {

lcci/02.02.Kth Node From End of List/Solution.js

@@ -11,14 +11,13 @@
  * @return {number}
  */
 var kthToLast = function (head, k) {
-    let fast = head,
-        slow = head;
-    for (let i = 0; i < k; i++) {
+    let [slow, fast] = [head, head];
+    while (k--) {
         fast = fast.next;
     }
-    while (fast != null) {
-        fast = fast.next;
+    while (fast !== null) {
         slow = slow.next;
+        fast = fast.next;
     }
     return slow.val;
 };

lcci/02.02.Kth Node From End of List/Solution.py

@@ -11,5 +11,6 @@ def kthToLast(self, head: ListNode, k: int) -> int:
         for _ in range(k):
             fast = fast.next
         while fast:
-            slow, fast = slow.next, fast.next
+            slow = slow.next
+            fast = fast.next
         return slow.val

lcci/02.02.Kth Node From End of List/Solution.ts

@@ -0,0 +1,23 @@
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function kthToLast(head: ListNode | null, k: number): number {
+    let [slow, fast] = [head, head];
+    while (k--) {
+        fast = fast.next;
+    }
+    while (fast !== null) {
+        slow = slow.next;
+        fast = fast.next;
+    }
+    return slow.val;
+}