some more problems solved

linked-list-cycle/sol.go

@@ -0,0 +1,26 @@
+package main
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+func hasCycle(head *ListNode) bool {
+	exists := map[*ListNode]bool{}
+	current := head
+	for current != nil {
+		exists[current] = true
+		current = current.Next
+		if exists[current] {
+			return true
+		}
+	}
+	return false
+}

linked-list-cycle/sol_O(1)_mem.go

@@ -0,0 +1,28 @@
+package main
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+// This solution uses O(1) memory, but
+// runtime duration is a bit more
+// unpredictable with a maximum complexity
+// of O(n^2) I think.
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+func hasCycle(head *ListNode) bool {
+	slow, fast := head, head
+	for fast != nil && fast.Next != nil {
+		slow, fast = slow.Next, fast.Next.Next
+		if slow == fast {
+			return true
+		}
+	}
+	return false
+}