feat(cipher/polybius): add fuzz test to polybius cipher (#600)

README.md

@@ -234,7 +234,7 @@ Read our [Contribution Guidelines](CONTRIBUTING.md) before you contribute.
 7. [`EditDistanceRecursive`](./dynamic/editdistance.go#L10):  EditDistanceRecursive is a naive implementation with exponential time complexity.
 8. [`IsSubsetSum`](./dynamic/subsetsum.go#L14): No description provided.
 9. [`Knapsack`](./dynamic/knapsack.go#L17):  Knapsack solves knapsack problem return maxProfit
-10. [`LongestCommonSubsequence`](./dynamic/longestcommonsubsequence.go#L12):  LongestCommonSubsequence function
+10. [`LongestCommonSubsequence`](./dynamic/longestcommonsubsequence.go#L13):  LongestCommonSubsequence function
 11. [`LongestIncreasingSubsequence`](./dynamic/longestincreasingsubsequence.go#L9):  LongestIncreasingSubsequence returns the longest increasing subsequence where all elements of the subsequence are sorted in increasing order
 12. [`LongestIncreasingSubsequenceGreedy`](./dynamic/longestincreasingsubsequencegreedy.go#L9):  LongestIncreasingSubsequenceGreedy is a function to find the longest increasing subsequence in a given array using a greedy approach. The dynamic programming approach is implemented alongside this one. Worst Case Time Complexity: O(nlogn) Auxiliary Space: O(n), where n is the length of the array(slice). Reference: https://www.geeksforgeeks.org/construction-of-longest-monotonically-increasing-subsequence-n-log-n/
 13. [`LpsDp`](./dynamic/longestpalindromicsubsequence.go#L25):  LpsDp function
@@ -778,6 +778,19 @@ Read our [Contribution Guidelines](CONTRIBUTING.md) before you contribute.
 3. [`Queue`](./structure/queue/queuelinkedlist.go#L19): No description provided.
 
 
+---
+</details><details>
+	<summary> <strong> rot13 </strong> </summary>	
+
+---
+
+#####  Package rot13 is a simple letter substitution cipher that replaces a letter with the 13th letter after it in the alphabet. ref: https://en.wikipedia.org/wiki/ROT13
+
+---
+##### Functions:
+
+1. [`FuzzRot13`](./cipher/rot13/rot13_test.go#L72): No description provided.
+
 ---
 </details><details>
 	<summary> <strong> rsa </strong> </summary>	

cipher/polybius/polybius.go

@@ -19,11 +19,22 @@ type Polybius struct {
 // If the size of "chars" is longer than "size",
 // "chars" are truncated to "size".
 func NewPolybius(key string, size int, chars string) (*Polybius, error) {
+	if size < 0 {
+		return nil, fmt.Errorf("provided size %d cannot be negative", size)
+	}
 	key = strings.ToUpper(key)
+	if size > len(chars) {
+		return nil, fmt.Errorf("provided size %d is too small to use to slice string %q of len %d", size, chars, len(chars))
+	}
+	for _, r := range chars {
+		if (r < 'a' || r > 'z') && (r < 'A' || r > 'Z') {
+			return nil, fmt.Errorf("provided string %q should only contain latin characters", chars)
+		}
+	}
 	chars = strings.ToUpper(chars)[:size]
-	for idx, ch := range chars {
-		if strings.Contains(chars[idx+1:], string(ch)) {
-			return nil, fmt.Errorf("\"chars\" contains same character: %c", ch)
+	for i, r := range chars {
+		if strings.ContainsRune(chars[i+1:], r) {
+			return nil, fmt.Errorf("%q contains same character %q", chars[i+1:], r)
 		}
 	}
 
@@ -63,7 +74,7 @@ func (p *Polybius) Decrypt(text string) (string, error) {
 func (p *Polybius) encipher(char rune) (string, error) {
 	index := strings.IndexRune(p.key, char)
 	if index < 0 {
-		return "", fmt.Errorf("%c does not exist in keys", char)
+		return "", fmt.Errorf("%q does not exist in keys", char)
 	}
 	row := index / p.size
 	col := index % p.size
@@ -83,5 +94,5 @@ func (p *Polybius) decipher(chars []rune) (string, error) {
 	if col < 0 {
 		return "", fmt.Errorf("%c does not exist in characters", chars[1])
 	}
-	return string([]rune(p.key)[row*p.size+col]), nil
+	return string(p.key[row*p.size+col]), nil
 }

cipher/polybius/polybius_test.go

@@ -3,6 +3,7 @@ package polybius
 import (
 	"fmt"
 	"log"
+	"strings"
 	"testing"
 )
 
@@ -54,7 +55,7 @@ func TestNewPolybius(t *testing.T) {
 			name: "invalid key", size: 5, characters: "HogeFuga", key: "abcdefghi", wantErr: "len(key): 9 must be as long as size squared: 25",
 		},
 		{
-			name: "invalid characters", size: 5, characters: "HogeH", key: "abcdefghijklmnopqrstuvwxy", wantErr: "\"chars\" contains same character: H",
+			name: "invalid characters", size: 5, characters: "HogeH", key: "abcdefghijklmnopqrstuvwxy", wantErr: "\"OGEH\" contains same character 'H'",
 		},
 	}
 
@@ -79,7 +80,7 @@ func TestPolybiusEncrypt(t *testing.T) {
 			name: "correct encryption", text: "HogeFugaPiyoSpam", want: "OGGFOOHFOHFHOOHHEHOEFFGFEEEHHHGG",
 		},
 		{
-			name: "invalid encryption", text: "hogz", want: "failed encipher: Z does not exist in keys",
+			name: "invalid encryption", text: "hogz", want: "failed encipher: 'Z' does not exist in keys",
 		},
 	}
 	// initialize
@@ -149,3 +150,41 @@ func TestPolybiusDecrypt(t *testing.T) {
 		})
 	}
 }
+
+func FuzzPolybius(f *testing.F) {
+	const (
+		size       = 5
+		characters = "HogeF"
+		key        = "abcdefghijklmnopqrstuvwxy"
+	)
+	f.Add(size, characters, key)
+	f.Fuzz(func(t *testing.T, size int, characters, key string) {
+		p, err := NewPolybius(key, size, characters)
+		switch {
+		case err == nil:
+		case strings.Contains(err.Error(), "cannot be negative"),
+			strings.Contains(err.Error(), "is too small"),
+			strings.Contains(err.Error(), "should only contain latin characters"),
+			strings.Contains(err.Error(), "contains same character"),
+			strings.Contains(err.Error(), "must be as long as size squared"):
+			return
+		default:
+			t.Fatalf("unexpected error when creating a new polybius variable: %v", err)
+		}
+		encrypted, err := p.Encrypt(characters)
+		switch {
+		case err == nil:
+		case strings.Contains(err.Error(), "does not exist in keys"):
+			return
+		default:
+			t.Fatalf("unexpected error during encryption: %v", err)
+		}
+		decrypted, err := p.Decrypt(encrypted)
+		if err != nil {
+			t.Fatalf("unexpected error during decryption: %v", err)
+		}
+		if decrypted != strings.ToUpper(characters) {
+			t.Errorf("Expecting output to match with %q but was %q", characters, decrypted)
+		}
+	})
+}