Add New String Interleave Class and Tests (TheAlgorithms#2032)

* added an Interleave class

* added interleaving sequence url

* Fixes: TheAlgorithms#2031

Co-authored-by: u6943702 <[email protected]>

Author: pdsla112

src/main/java/com/string/Interleave.java

@@ -0,0 +1,151 @@
+package com.string;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class Interleave {
+    @Test
+    public void testInterleaveRegularString() {
+        String string1 = "Hello";
+        String string2 = "World";
+        String expected = "HWeolrllod";
+        String actual = interleave(string1, string2);
+        assertEquals("Incorrect result from method.", expected, actual);
+    }
+
+    @Test
+    public void testInterleaveEmptyString() {
+        String string1 = "";
+        String string2 = "";
+        String string3 = "a";
+        String string4 = "abc";
+        String expected1 = "";
+        String actual1 = interleave(string1, string2);
+        String expected2 = "a";
+        String actual2 = interleave(string1, string3);
+        String expected3 = "abc";
+        String actual3 = interleave(string1, string4);
+        assertEquals("Incorrect result from method.", expected1, actual1);
+        assertEquals("Incorrect result from method.", expected2, actual2);
+        assertEquals("Incorrect result from method.", expected3, actual3);
+    }
+
+    @Test
+    public void testInterleaveSingleString() {
+        String string1 = "a";
+        String string2 = "b";
+        String expected = "ab";
+        String actual = interleave(string1, string2);
+        assertEquals("Incorrect result from method.", expected, actual);
+    }
+
+    @Test
+    public void testInterleaveIntString() {
+        String string1 = "1";
+        String string2 = "7";
+        String expected = "17";
+        String actual = interleave(string1, string2);
+        assertEquals("Incorrect result from method.", expected, actual);
+    }
+
+    @Test
+    public void testInterleaveMixedString() {
+        String string1 = "1a2b3c4d";
+        String string2 = "5e6f7g8h";
+        String expected = "15ae26bf37cg48dh";
+        String actual = interleave(string1, string2);
+        assertEquals("Incorrect result from method.", expected, actual);
+    }
+
+    @Test
+    public void testInterleaveSymbols() {
+        String string1 = "a@b%c/";
+        String string2 = "d#e$g%.";
+        String expected = "ad@#be%$cg/%.";
+        String actual = interleave(string1, string2);
+        assertEquals("Incorrect result from method.", expected, actual);
+    }
+
+    @Test
+    public void testInterleaveSpaces() {     // This string interleave algorithm defines a space as a valid character.
+        String string1 = " ";
+        String string2 = "a";
+        String string3 = "5 g";
+        String string4 = " 4 d ";
+        String expected1 = " a";
+        String actual1 = interleave(string1, string2);
+        String expected2 = "a5 g";
+        String actual2 = interleave(string2, string3);
+        String expected3 = "5  4g d ";
+        String actual3 = interleave(string3, string4);
+        assertEquals("Incorrect result from method.", expected1, actual1);
+        assertEquals("Incorrect result from method.", expected2, actual2);
+        assertEquals("Incorrect result from method.", expected3, actual3);
+    }
+
+    /**
+     * This method "interweaves" two input strings one character at a time. The first character of the
+     * first parameter string always starts the resulting string, unless that character is a space or is empty.
+     * This string interleaving method takes a space in a string (e.g. " ") into consideration.
+     *
+     * For example, if string1 = "abc" and string2 = "def", then the result would be "adbecf", as the first character
+     * of the string1 is 'a', then the first character of string2 is 'd', and so forth.
+     *
+     * For more information on interleaving, check out: https://en.wikipedia.org/wiki/Interleave_sequence
+     *
+     * @param string1
+     * @param string2
+     * @return string resulting from the interweaving of the two input strings; string1 and string2.
+     */
+    public String interleave(String string1, String string2) {
+        String result = "";     // The final interleaved string to return.
+        List<Character> list1 = new ArrayList<>();     // The ArrayList of string1, with each character being an individual element.
+        List<Character> list2 = new ArrayList<>();     // The ArrayList of string2, in a similar manner as above.
+
+        for (int i = 0; i < string1.length(); i++)     // Convert string1 into list1.
+            list1.add(string1.charAt(i));
+
+        for (int i = 0; i < string2.length(); i++)     // Convert string2 into list2.
+            list2.add(string2.charAt(i));
+
+        if (string1.length() == string2.length()) {     // Interleaving when string1 and string2 are equal length.
+            for (int j = 0; j < list1.size(); j++) {
+                result = result + list1.get(j);
+                result = result + list2.get(j);
+            }
+            return result;
+        }
+
+        if (string1.length() > string2.length()) {     // Interleaving when string1 is longer than string2.
+            while (list2.size() > 0) {
+                result = result + list1.get(0);
+                list1.remove(0);
+                result = result + list2.get(0);
+                list2.remove(0);
+            }
+            for (char character : list1) {     // Concatenate the rest of the characters in list1 to the result.
+                result = result + character;
+            }
+            return result;
+        }
+
+        if (string2.length() > string1.length()) {     // Interleaving when string2 is longer than string1.
+            while (list1.size() > 0) {
+                result = result + list1.get(0);
+                list1.remove(0);
+                result = result + list2.get(0);
+                list2.remove(0);
+            }
+            for (char character : list2) {     // Concatenate the rest of the characters in list2 to the result.
+                result = result + character;
+            }
+            return result;
+        }
+
+        return result;
+    }
+}