Implementation of zip function #72 (#92)

* #72: First test passing

* #72: Second test passing

* #72: Third test passing

* #72: Added extra assertion

* #72: Fixed wrong test

* #72: Fixed wrong test

* #72: Added fourth test (passing)

* #72: fixed typo in test name

* #72: added fifth test

* #72: fixed test names

* #72: refactored for multiple inputs

* #72: added extra test cases and documentation

* #72: addressed @shekhargulati comments

src/main/java/strman/Strman.java

@@ -33,6 +33,8 @@ import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Stream;
 
+import static java.lang.Math.min;
+import static java.util.Collections.emptyList;
 import static java.util.function.Function.identity;
 import static java.util.stream.Collectors.*;
 
@@ -1334,5 +1336,57 @@ public abstract class Strman {
         return countSubstr(value.substring(offset), subStr, allowOverlapping, ++count);
     }
 
+    /**
+     * Aggregates the contents of n strings into a single list of tuples.
+     *
+     * @param inputs A list of strings.
+     * @return A list of strings if none of the strings in the input is null or empty.
+     * An empty list otherwise.
+     */
+    public static List<String> zip(String... inputs) {
+        if (inputs.length == 1) {
+            return inputs[0].codePoints()
+                    .mapToObj(Character::toChars)
+                    .map(String::new)
+                    .collect(toList());
+        }
+
+        int minLength = calculateMinLength(inputs);
+
+        if (minLength == -1) {
+            return emptyList();
+        }
+
+        List<String> zipped = new ArrayList<>(minLength);
+
+        for (int elementIndex = 0; elementIndex < minLength; ++elementIndex) {
+            StringBuilder tuple = new StringBuilder();
+
+            for (int inputIndex = 0; inputIndex < inputs.length; ++inputIndex) {
+                tuple.append(inputs[inputIndex].charAt(elementIndex));
+            }
+
+            zipped.add(tuple.toString());
+        }
+
+        return zipped;
+    }
+
+    private static int calculateMinLength(String[] inputs) {
+        if (inputs.length == 0) {
+            return -1;
+        }
+
+        int minLength = Integer.MAX_VALUE;
+
+        for (String input : inputs) {
+            if (isNullOrEmpty(input)) {
+                return -1;
+            }
+            minLength = min(minLength, input.length());
+        }
+
+        return minLength;
+    }
 }