diff --git a/longest-substring-without-repeating-characters/neverlish.go b/longest-substring-without-repeating-characters/neverlish.go
new file mode 100644
index 000000000..98bbccc82
--- /dev/null
+++ b/longest-substring-without-repeating-characters/neverlish.go
@@ -0,0 +1,49 @@
+// 시간복잡도: O(n^2)
+// 공간복잡도: O(n)
+
+package main
+
+import "testing"
+
+func TestLengthOfLongestSubstring(t *testing.T) {
+	result1 := lengthOfLongestSubstring("abcabcbb")
+
+	if result1 != 3 {
+		t.Errorf("Expected 3, but got %v", result1)
+	}
+
+	result2 := lengthOfLongestSubstring("bbbbb")
+	if result2 != 1 {
+		t.Errorf("Expected 1, but got %v", result2)
+	}
+
+	result3 := lengthOfLongestSubstring("pwwkew")
+	if result3 != 3 {
+		t.Errorf("Expected 3, but got %v", result3)
+	}
+
+	result4 := lengthOfLongestSubstring("")
+	if result4 != 0 {
+		t.Errorf("Expected 0, but got %v", result4)
+	}
+}
+
+func lengthOfLongestSubstring(s string) int {
+	result := 0
+
+	for i := 0; i < len(s); i++ {
+		m := make(map[rune]bool)
+		for j := i; j < len(s); j++ {
+			if _, ok := m[rune(s[j])]; ok {
+				break
+			}
+			m[rune(s[j])] = true
+		}
+
+		if len(m) > result {
+			result = len(m)
+		}
+	}
+
+	return result
+}
diff --git a/number-of-islands/neverlish.go b/number-of-islands/neverlish.go
new file mode 100644
index 000000000..b1459c265
--- /dev/null
+++ b/number-of-islands/neverlish.go
@@ -0,0 +1,58 @@
+// 시간복잡도: O(n^2)
+// 공간복잡도: O(n)
+
+package main
+
+import "testing"
+
+func TestNumIslands(t *testing.T) {
+	result1 := numIslands([][]byte{
+		{'1', '1', '1', '1', '0'},
+		{'1', '1', '0', '1', '0'},
+		{'1', '1', '0', '0', '0'},
+		{'0', '0', '0', '0', '0'},
+	})
+
+	if result1 != 1 {
+		t.Errorf("Expected 1, but got %v", result1)
+	}
+
+	result2 := numIslands([][]byte{
+		{'1', '1', '0', '0', '0'},
+		{'1', '1', '0', '0', '0'},
+		{'0', '0', '1', '0', '0'},
+		{'0', '0', '0', '1', '1'},
+	})
+
+	if result2 != 3 {
+		t.Errorf("Expected 3, but got %v", result2)
+	}
+}
+
+func dfs(grid [][]byte, i, j int) {
+	if i < 0 || j < 0 || i >= len(grid) || j >= len(grid[i]) || grid[i][j] == '0' {
+		return
+	}
+
+	grid[i][j] = '0'
+
+	dfs(grid, i-1, j)
+	dfs(grid, i+1, j)
+	dfs(grid, i, j-1)
+	dfs(grid, i, j+1)
+}
+
+func numIslands(grid [][]byte) int {
+	result := 0
+
+	for i := 0; i < len(grid); i++ {
+		for j := 0; j < len(grid[i]); j++ {
+			if grid[i][j] == '1' {
+				result++
+				dfs(grid, i, j)
+			}
+		}
+	}
+
+	return result
+}
diff --git a/reverse-linked-list/neverlish.go b/reverse-linked-list/neverlish.go
new file mode 100644
index 000000000..4fd989ae3
--- /dev/null
+++ b/reverse-linked-list/neverlish.go
@@ -0,0 +1,63 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(1)
+
+package main
+
+import "testing"
+
+func TestReverseList(t *testing.T) {
+	result1 := reverseList(&ListNode{
+		Val: 1,
+		Next: &ListNode{
+			Val: 2,
+			Next: &ListNode{
+				Val: 3,
+				Next: &ListNode{
+					Val: 4,
+					Next: &ListNode{
+						Val:  5,
+						Next: nil,
+					},
+				},
+			},
+		},
+	})
+
+	if result1.Val != 5 {
+		t.Errorf("Expected 5, but got %v", result1.Val)
+	}
+
+	if result1.Next.Val != 4 {
+		t.Errorf("Expected 4, but got %v", result1.Next.Val)
+	}
+
+	if result1.Next.Next.Val != 3 {
+		t.Errorf("Expected 3, but got %v", result1.Next.Next.Val)
+	}
+
+	if result1.Next.Next.Next.Val != 2 {
+		t.Errorf("Expected 2, but got %v", result1.Next.Next.Next.Val)
+	}
+
+	if result1.Next.Next.Next.Next.Val != 1 {
+		t.Errorf("Expected 1, but got %v", result1.Next.Next.Next.Next.Val)
+	}
+}
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+func reverseList(head *ListNode) *ListNode {
+	var prev *ListNode
+
+	for head != nil {
+		next := head.Next
+		head.Next = prev
+		prev = head
+		head = next
+	}
+
+	return prev
+}