From dbd72eb1000e19ed4595b1432e8ab4a21fa7da67 Mon Sep 17 00:00:00 2001
From: Billy Zaelani Malik <m.billyzaelani@gmail.com>
Date: Wed, 13 Dec 2023 11:53:20 +0700
Subject: [PATCH] geeksforgeeks: add lexicographically next string

---
 .../lexicographically-next-string/README.md   | 15 ++++++++++
 .../lexicographically-next-string/solution.go | 23 +++++++++++++++
 .../solution_test.go                          | 29 +++++++++++++++++++
 3 files changed, 67 insertions(+)
 create mode 100644 geeksforgeeks/lexicographically-next-string/README.md
 create mode 100644 geeksforgeeks/lexicographically-next-string/solution.go
 create mode 100644 geeksforgeeks/lexicographically-next-string/solution_test.go

diff --git a/geeksforgeeks/lexicographically-next-string/README.md b/geeksforgeeks/lexicographically-next-string/README.md
new file mode 100644
index 0000000..bb22dde
--- /dev/null
+++ b/geeksforgeeks/lexicographically-next-string/README.md
@@ -0,0 +1,15 @@
+# Lexicographically next string
+
+Given a string, find lexicographically next string.
+If string is empty, we return ‘a’.
+If string contains all characters as ‘z’, we append ‘a’ at the end.
+Otherwise we find first character from end which is not z and increment it.
+
+## Copyright Notice
+
+This problem is based on [content](https://www.geeksforgeeks.org/lexicographically-next-string/)
+from [GeeksforGeeks](https://www.geeksforgeeks.org)
+written by GeeksforGeeks
+and subject to [GeeksforGeeks copyright](https://www.geeksforgeeks.org/legal/copyright-information/).
+The original content from GeeksforGeeks and any modifications made here are attributed to GeeksforGeeks contributors,
+and this work is shared under [CC BY-SA 4.0](../LICENSE).
diff --git a/geeksforgeeks/lexicographically-next-string/solution.go b/geeksforgeeks/lexicographically-next-string/solution.go
new file mode 100644
index 0000000..ca6ce26
--- /dev/null
+++ b/geeksforgeeks/lexicographically-next-string/solution.go
@@ -0,0 +1,23 @@
+package lexicographically_next_string
+
+import "strings"
+
+func Solution(s string) string {
+	i := len(s) - 1
+	for i >= 0 && s[i] == 'z' {
+		i--
+	}
+
+	if i == -1 {
+		return s + "a"
+	}
+
+	j := 0
+	return strings.Map(func(r rune) rune {
+		if j == i {
+			r += 1
+		}
+		j++
+		return r
+	}, s)
+}
diff --git a/geeksforgeeks/lexicographically-next-string/solution_test.go b/geeksforgeeks/lexicographically-next-string/solution_test.go
new file mode 100644
index 0000000..9207ac4
--- /dev/null
+++ b/geeksforgeeks/lexicographically-next-string/solution_test.go
@@ -0,0 +1,29 @@
+package lexicographically_next_string_test
+
+import (
+	"testing"
+
+	sut "github.com/minizilla/minmax/geeksforgeeks/lexicographically-next-string"
+	"github.com/minizilla/testr"
+)
+
+func TestLexicographicallyNextString(t *testing.T) {
+	tests := map[string]struct {
+		in, out string
+	}{
+		"empty": {"", "a"},
+		"a":     {"a", "b"},
+		"z":     {"z", "za"},
+		"ab":    {"ab", "ac"},
+		"az":    {"az", "bz"},
+		"zz":    {"zz", "zza"},
+	}
+
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
+			assert := testr.New(t)
+			out := sut.Solution(tc.in)
+			assert.Equal(out, tc.out)
+		})
+	}
+}