[bus710] Week 09

linked-list-cycle/bus710.go

@@ -0,0 +1,94 @@
+package hello
+
+import "testing"
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+// // Version 1
+// func hasCycle(head *ListNode) bool {
+// 	if head == nil {
+// 		return false
+// 	}
+// 	return call(head, make(map[*ListNode]int, 0))
+// }
+//
+// func call(h *ListNode, m map[*ListNode]int) bool {
+// 	if h.Next == nil {
+// 		return false
+// 	}
+// 	if _, ok := m[h]; ok {
+// 		return true
+// 	}
+// 	m[h] = 1
+// 	return call(h.Next, m)
+// }
+
+// Version 2
+func hasCycle(head *ListNode) bool {
+	if head == nil {
+		return false
+	}
+	m := map[*ListNode]int{}
+	for head.Next != nil {
+		if _, ok := m[head]; !ok {
+			m[head] = 1
+		} else {
+			return true
+		}
+		head = head.Next
+	}
+	return false
+}
+
+func Test_hasCycle(t *testing.T) {
+	// Case 0 list
+	c0_3 := &ListNode{Val: -4}
+	c0_2 := &ListNode{Val: 0, Next: c0_3}
+	c0_1 := &ListNode{Val: 2, Next: c0_2}
+	c0_0 := &ListNode{Val: 3, Next: c0_1}
+	c0_3.Next = c0_1
+
+	// Case 1 list
+	c1_1 := &ListNode{Val: 2}
+	c1_0 := &ListNode{Val: 1, Next: c1_1}
+	c1_1.Next = c1_0
+
+	// Case 2 list
+	c2_0 := &ListNode{Val: 1}
+
+	type args struct {
+		head *ListNode
+	}
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{
+			name: "case 0",
+			args: args{head: c0_0},
+			want: true,
+		},
+		{
+			name: "case 1",
+			args: args{head: c1_0},
+			want: true,
+		},
+		{
+			name: "case 2",
+			args: args{head: c2_0},
+			want: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := hasCycle(tt.args.head)
+			if got != tt.want {
+				t.Errorf("hasCycle() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}