General performance improvement (#6078)

Author: mosbat

src/main/java/com/thealgorithms/ciphers/AES.java

@@ -2418,8 +2418,6 @@ public static BigInteger scheduleCore(BigInteger t, int rconCounter) {
             rBytes = new StringBuilder(rBytes.substring(0, i * 2) + currentByteBits + rBytes.substring((i + 1) * 2));
         }
 
-        // t = new BigInteger(rBytes, 16);
-        // return t;
         return new BigInteger(rBytes.toString(), 16);
     }
 

src/main/java/com/thealgorithms/ciphers/AffineCipher.java

@@ -34,19 +34,19 @@ private AffineCipher() {
      */
     static String encryptMessage(char[] msg) {
         // Cipher Text initially empty
-        String cipher = "";
+        StringBuilder cipher = new StringBuilder();
         for (int i = 0; i < msg.length; i++) {
             // Avoid space to be encrypted
             /* applying encryption formula ( a * x + b ) mod m
             {here x is msg[i] and m is 26} and added 'A' to
             bring it in the range of ASCII alphabet [65-90 | A-Z] */
             if (msg[i] != ' ') {
-                cipher += (char) ((((a * (msg[i] - 'A')) + b) % 26) + 'A');
+                cipher.append((char) ((((a * (msg[i] - 'A')) + b) % 26) + 'A'));
             } else { // else simply append space character
-                cipher += msg[i];
+                cipher.append(msg[i]);
             }
         }
-        return cipher;
+        return cipher.toString();
     }
 
     /**
@@ -56,7 +56,7 @@ static String encryptMessage(char[] msg) {
      * @return the decrypted plaintext message
      */
     static String decryptCipher(String cipher) {
-        String msg = "";
+        StringBuilder msg = new StringBuilder();
         int aInv = 0;
         int flag;
 
@@ -75,13 +75,13 @@ static String decryptCipher(String cipher) {
             {here x is cipher[i] and m is 26} and added 'A'
             to bring it in the range of ASCII alphabet [65-90 | A-Z] */
             if (cipher.charAt(i) != ' ') {
-                msg += (char) (((aInv * ((cipher.charAt(i) - 'A') - b + 26)) % 26) + 'A');
+                msg.append((char) (((aInv * ((cipher.charAt(i) - 'A') - b + 26)) % 26) + 'A'));
             } else { // else simply append space character
-                msg += cipher.charAt(i);
+                msg.append(cipher.charAt(i));
             }
         }
 
-        return msg;
+        return msg.toString();
     }
 
     // Driver code

src/main/java/com/thealgorithms/ciphers/Blowfish.java

@@ -1078,7 +1078,7 @@ public class Blowfish {
      * @return String object which is a binary representation of the hex number passed as parameter
      */
     private String hexToBin(String hex) {
-        String binary = "";
+        StringBuilder binary = new StringBuilder();
         long num;
         String binary4B;
         int n = hex.length();
@@ -1089,9 +1089,9 @@ private String hexToBin(String hex) {
             binary4B = "0000" + binary4B;
 
             binary4B = binary4B.substring(binary4B.length() - 4);
-            binary += binary4B;
+            binary.append(binary4B);
         }
-        return binary;
+        return binary.toString();
     }
 
     /**
@@ -1103,12 +1103,12 @@ private String hexToBin(String hex) {
      */
     private String binToHex(String binary) {
         long num = Long.parseUnsignedLong(binary, 2);
-        String hex = Long.toHexString(num);
+        StringBuilder hex = new StringBuilder(Long.toHexString(num));
         while (hex.length() < (binary.length() / 4)) {
-            hex = "0" + hex;
+            hex.insert(0, "0");
         }
 
-        return hex;
+        return hex.toString();
     }
 
     /**
@@ -1121,12 +1121,12 @@ private String binToHex(String binary) {
     private String xor(String a, String b) {
         a = hexToBin(a);
         b = hexToBin(b);
-        String ans = "";
+        StringBuilder ans = new StringBuilder();
         for (int i = 0; i < a.length(); i++) {
-            ans += (char) (((a.charAt(i) - '0') ^ (b.charAt(i) - '0')) + '0');
+            ans.append((char) (((a.charAt(i) - '0') ^ (b.charAt(i) - '0')) + '0'));
         }
-        ans = binToHex(ans);
-        return ans;
+        ans = new StringBuilder(binToHex(ans.toString()));
+        return ans.toString();
     }
 
     /**

src/main/java/com/thealgorithms/conversions/AnyBaseToAnyBase.java

@@ -136,7 +136,7 @@ public static String base2base(String n, int b1, int b2) {
         int decimalValue = 0;
         int charB2;
         char charB1;
-        String output = "";
+        StringBuilder output = new StringBuilder();
         // Go through every character of n
         for (int i = 0; i < n.length(); i++) {
             // store the character in charB1
@@ -167,15 +167,15 @@ public static String base2base(String n, int b1, int b2) {
             // If the remainder is a digit < 10, simply add it to
             // the left side of the new number.
             if (decimalValue % b2 < 10) {
-                output = decimalValue % b2 + output;
+                output.insert(0, decimalValue % b2);
             } // If the remainder is >= 10, add a character with the
             // corresponding value to the new number. (A = 10, B = 11, C = 12, ...)
             else {
-                output = (char) ((decimalValue % b2) + 55) + output;
+                output.insert(0, (char) ((decimalValue % b2) + 55));
             }
             // Divide by the new base again
             decimalValue /= b2;
         }
-        return output;
+        return output.toString();
     }
 }

src/main/java/com/thealgorithms/conversions/HexaDecimalToBinary.java

@@ -52,9 +52,11 @@ public String convert(String numHex) {
      */
     public String completeDigits(String binNum) {
         final int byteSize = 8;
-        while (binNum.length() < byteSize) {
-            binNum = "0" + binNum;
+        StringBuilder binNumBuilder = new StringBuilder(binNum);
+        while (binNumBuilder.length() < byteSize) {
+            binNumBuilder.insert(0, "0");
         }
+        binNum = binNumBuilder.toString();
         return binNum;
     }
 }

src/main/java/com/thealgorithms/datastructures/graphs/FloydWarshall.java

@@ -42,9 +42,7 @@ public FloydWarshall(int numberofvertices) {
     public void floydwarshall(int[][] adjacencyMatrix) {
         // Initialize the distance matrix with the adjacency matrix.
         for (int source = 1; source <= numberofvertices; source++) {
-            for (int destination = 1; destination <= numberofvertices; destination++) {
-                distanceMatrix[source][destination] = adjacencyMatrix[source][destination];
-            }
+            System.arraycopy(adjacencyMatrix[source], 1, distanceMatrix[source], 1, numberofvertices);
         }
         for (int intermediate = 1; intermediate <= numberofvertices; intermediate++) {
             for (int source = 1; source <= numberofvertices; source++) {

src/main/java/com/thealgorithms/datastructures/lists/SinglyLinkedList.java

@@ -403,7 +403,7 @@ public static void main(String[] arg) {
         SinglyLinkedList list = new SinglyLinkedList();
         assert list.isEmpty();
         assert list.size() == 0 && list.count() == 0;
-        assert list.toString().equals("");
+        assert list.toString().isEmpty();
 
         /* Test insert function */
         list.insertHead(5);

src/main/java/com/thealgorithms/datastructures/trees/GenericTree.java

@@ -23,6 +23,7 @@ private static final class Node {
     }
 
     private final Node root;
+
     public GenericTree() { // Constructor
         Scanner scn = new Scanner(System.in);
         root = createTreeG(null, 0, scn);
@@ -225,8 +226,6 @@ private void removeleaves(Node node) {
         for (int i = 0; i < node.child.size(); i++) {
             if (node.child.get(i).child.size() == 0) {
                 arr.add(i);
-                // node.child.remove(i);
-                // i--;
             } else {
                 removeleaves(node.child.get(i));
             }

src/main/java/com/thealgorithms/graph/StronglyConnectedComponentOptimized.java

@@ -1,3 +1,5 @@
+package com.thealgorithms.graph;
+
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;

src/main/java/com/thealgorithms/maths/NthUglyNumber.java

@@ -1,7 +1,8 @@
 package com.thealgorithms.maths;
 
+import static java.util.Collections.singletonList;
+
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Map;
 import org.apache.commons.lang3.tuple.MutablePair;
 
@@ -16,7 +17,7 @@
  *     - the base [2, 3, 5] ugly numbers are the same as base [5, 6, 2, 3, 5] ugly numbers
  */
 public class NthUglyNumber {
-    private ArrayList<Long> uglyNumbers = new ArrayList<>(Arrays.asList(1L));
+    private ArrayList<Long> uglyNumbers = new ArrayList<>(singletonList(1L));
     private ArrayList<MutablePair<Integer, Integer>> positions = new ArrayList<>();
 
     /**