python3 解法, 执行用时: 48 ms, 内存消耗: 18.9 MB, 提交时间: 2022-11-30 12:58:11

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def detectCycle(self, head: ListNode) -> ListNode:
        seen = dict()
        while head:
            if head in seen: return head
            seen[head] = 1
            head = head.next
        return None

python3 解法, 执行用时: 60 ms, 内存消耗: 18.5 MB, 提交时间: 2022-11-30 12:55:36

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def detectCycle(self, head: ListNode) -> ListNode:
        slow, fast = head, head
        while fast:
            slow = slow.next
            if fast.next == None:
                return None
            
            fast = fast.next.next
            if fast == slow:
                p = head
                while p != slow:
                    p = p.next
                    slow = slow.next
                
                return p
        return None

golang 解法, 执行用时: 4 ms, 内存消耗: 3.5 MB, 提交时间: 2022-11-30 12:52:27

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func detectCycle(head *ListNode) *ListNode {
    slow, fast := head, head
    for fast != nil {
        slow = slow.Next
        if fast.Next == nil {
            return nil
        }
        fast = fast.Next.Next
        if fast == slow {
            p := head
            for p != slow {
                p = p.Next
                slow = slow.Next
            }
            return p
        }
    }
    return nil
}

javascript 解法, 执行用时: 60 ms, 内存消耗: 43.3 MB, 提交时间: 2022-11-30 12:52:09

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var detectCycle = function(head) {
    if (head === null) {
        return null;
    }
    let slow = head, fast = head;
    while (fast !== null) {
        slow = slow.next;
        if (fast.next !== null) {
            fast = fast.next.next;
        } else {
            return null;
        }
        if (fast === slow) {
            let ptr = head;
            while (ptr !== slow) {
                ptr = ptr.next;
                slow = slow.next;
            }
            return ptr;
        }
    }
    return null;
};

javascript 解法, 执行用时: 80 ms, 内存消耗: 44 MB, 提交时间: 2022-11-30 12:51:51

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var detectCycle = function(head) {
    const visited = new Set();
    while (head !== null) {
        if (visited.has(head)) {
            return head;
        }
        visited.add(head);
        head = head.next;
    }
    return null;
};

golang 解法, 执行用时: 8 ms, 内存消耗: 4.8 MB, 提交时间: 2022-11-30 12:51:30

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func detectCycle(head *ListNode) *ListNode {
    seen := map[*ListNode]struct{}{}
    for head != nil {
        if _, ok := seen[head]; ok {
            return head
        }
        seen[head] = struct{}{}
        head = head.Next
    }
    return nil
}