diff --git a/leetcode/0382.Linked-List-Random-Node/382. Linked List Random Node.go b/leetcode/0382.Linked-List-Random-Node/382. Linked List Random Node.go new file mode 100644 index 00000000..0e54f754 --- /dev/null +++ b/leetcode/0382.Linked-List-Random-Node/382. Linked List Random Node.go @@ -0,0 +1,46 @@ +package leetcode + +import ( + "math/rand" + + "github.com/halfrost/LeetCode-Go/structures" +) + +// ListNode define +type ListNode = structures.ListNode + +/** + * Definition for singly-linked list. + * type ListNode struct { + * Val int + * Next *ListNode + * } + */ +type Solution struct { + head *ListNode +} + +/** @param head The linked list's head. + Note that the head is guaranteed to be not null, so it contains at least one node. */ +func Constructor(head *ListNode) Solution { + return Solution{head: head} +} + +/** Returns a random node's value. */ +func (this *Solution) GetRandom() int { + scope, selectPoint, curr := 1, 0, this.head + for curr != nil { + if rand.Float64() < 1.0/float64(scope) { + selectPoint = curr.Val + } + scope += 1 + curr = curr.Next + } + return selectPoint +} + +/** + * Your Solution object will be instantiated and called as such: + * obj := Constructor(head); + * param_1 := obj.GetRandom(); + */ diff --git a/leetcode/0382.Linked-List-Random-Node/382. Linked List Random Node_test.go b/leetcode/0382.Linked-List-Random-Node/382. Linked List Random Node_test.go new file mode 100644 index 00000000..f3371344 --- /dev/null +++ b/leetcode/0382.Linked-List-Random-Node/382. Linked List Random Node_test.go @@ -0,0 +1,28 @@ +package leetcode + +import ( + "fmt" + "testing" + + "github.com/halfrost/LeetCode-Go/structures" +) + +func Test_Problem382(t *testing.T) { + header := structures.Ints2List([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 0}) + obj := Constructor(header) + fmt.Printf("obj = %v\n", structures.List2Ints(header)) + param1 := obj.GetRandom() + fmt.Printf("param_1 = %v\n", param1) + param1 = obj.GetRandom() + fmt.Printf("param_1 = %v\n", param1) + param1 = obj.GetRandom() + fmt.Printf("param_1 = %v\n", param1) + param1 = obj.GetRandom() + fmt.Printf("param_1 = %v\n", param1) + param1 = obj.GetRandom() + fmt.Printf("param_1 = %v\n", param1) + param1 = obj.GetRandom() + fmt.Printf("param_1 = %v\n", param1) + + fmt.Printf("\n\n\n") +} diff --git a/leetcode/0382.Linked-List-Random-Node/README.md b/leetcode/0382.Linked-List-Random-Node/README.md new file mode 100644 index 00000000..db5ecc06 --- /dev/null +++ b/leetcode/0382.Linked-List-Random-Node/README.md @@ -0,0 +1,105 @@ +# [382. Linked List Random Node](https://leetcode.com/problems/linked-list-random-node/) + + +## 题目 + +Given a singly linked list, return a random node's value from the linked list. Each node must have the **same probability** of being chosen. + +Implement the `Solution` class: + +- `Solution(ListNode head)` Initializes the object with the integer array nums. +- `int getRandom()` Chooses a node randomly from the list and returns its value. All the nodes of the list should be equally likely to be choosen. + +**Example 1:** + +![https://assets.leetcode.com/uploads/2021/03/16/getrand-linked-list.jpg](https://assets.leetcode.com/uploads/2021/03/16/getrand-linked-list.jpg) + +``` +Input +["Solution", "getRandom", "getRandom", "getRandom", "getRandom", "getRandom"] +[[[1, 2, 3]], [], [], [], [], []] +Output +[null, 1, 3, 2, 2, 3] + +Explanation +Solution solution = new Solution([1, 2, 3]); +solution.getRandom(); // return 1 +solution.getRandom(); // return 3 +solution.getRandom(); // return 2 +solution.getRandom(); // return 2 +solution.getRandom(); // return 3 +// getRandom() should return either 1, 2, or 3 randomly. Each element should have equal probability of returning. + +``` + +**Constraints:** + +- The number of nodes in the linked list will be in the range `[1, 104]`. +- `-10^4 <= Node.val <= 10^4` +- At most `10^4` calls will be made to `getRandom`. + +**Follow up:** + +- What if the linked list is extremely large and its length is unknown to you? +- Could you solve this efficiently without using extra space? + +## 题目大意 + +给定一个单链表,随机选择链表的一个节点,并返回相应的节点值。保证每个节点被选的概率一样。 + +进阶: 如果链表十分大且长度未知,如何解决这个问题?你能否使用常数级空间复杂度实现? + +## 解题思路 + +- rand.Float64() 可以返回 [0.0,1.0) 之间的随机数。利用这个函数完成我们的随机化取节点的过程。 + +## 代码 + +```go +package leetcode + +import ( + "math/rand" + + "github.com/halfrost/LeetCode-Go/structures" +) + +// ListNode define +type ListNode = structures.ListNode + +/** + * Definition for singly-linked list. + * type ListNode struct { + * Val int + * Next *ListNode + * } + */ +type Solution struct { + head *ListNode +} + +/** @param head The linked list's head. + Note that the head is guaranteed to be not null, so it contains at least one node. */ +func Constructor(head *ListNode) Solution { + return Solution{head: head} +} + +/** Returns a random node's value. */ +func (this *Solution) GetRandom() int { + scope, selectPoint, curr := 1, 0, this.head + for curr != nil { + if rand.Float64() < 1.0/float64(scope) { + selectPoint = curr.Val + } + scope += 1 + curr = curr.Next + } + return selectPoint +} + +/** + * Your Solution object will be instantiated and called as such: + * obj := Constructor(head); + * param_1 := obj.GetRandom(); + */ +``` \ No newline at end of file