Add: Linked List Cycle

Author: openset

problems/linked-list-cycle/linked_list_cycle.go

@@ -1 +1,23 @@
 package linked_list_cycle
+
+import . "github.com/openset/leetcode/internal/kit"
+
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+func hasCycle(head *ListNode) bool {
+	for p1, p2 := head, head; p1 != nil; p1 = p1.Next {
+		if p2 != nil && p2.Next != nil {
+			if p2 = p2.Next.Next; p1 == p2 {
+				return true
+			}
+		} else {
+			return false
+		}
+	}
+	return false
+}

problems/linked-list-cycle/linked_list_cycle_test.go

@@ -1 +1,50 @@
 package linked_list_cycle
+
+import (
+	"testing"
+
+	. "github.com/openset/leetcode/internal/kit"
+)
+
+type caseType struct {
+	input    []int
+	pos      int
+	expected bool
+}
+
+func TestHasCycle(t *testing.T) {
+	tests := [...]caseType{
+		{
+			input:    []int{3, 2, 0, -4},
+			pos:      1,
+			expected: true,
+		},
+		{
+			input:    []int{1, 2},
+			pos:      0,
+			expected: true,
+		},
+		{
+			input:    []int{1},
+			pos:      -1,
+			expected: false,
+		},
+	}
+	for _, tc := range tests {
+		input := SliceInt2ListNode(tc.input)
+		p, curr := input, input
+		for i := 0; curr != nil && tc.pos >= 0; i, curr = i+1, curr.Next {
+			if i == tc.pos {
+				p = curr
+			}
+			if curr.Next == nil {
+				curr.Next = p
+				break
+			}
+		}
+		output := hasCycle(input)
+		if output != tc.expected {
+			t.Fatalf("input: %v, output: %v, expected: %v", tc.input, output, tc.expected)
+		}
+	}
+}