Merge branch 'master' into cleanup/RangeInSortedArray

Author: DenizAltunkapan

src/main/java/com/thealgorithms/stacks/LargestRectangle.java

@@ -3,36 +3,50 @@
 import java.util.Stack;
 
 /**
+ * Utility class to calculate the largest rectangle area in a histogram.
+ * Each bar's width is assumed to be 1 unit.
  *
- * @author mohd rameez github.com/rameez471
+ * <p>This implementation uses a monotonic stack to efficiently calculate
+ * the area of the largest rectangle that can be formed from the histogram bars.</p>
+ *
+ * <p>Example usage:
+ * <pre>{@code
+ *     int[] heights = {2, 1, 5, 6, 2, 3};
+ *     String area = LargestRectangle.largestRectangleHistogram(heights);
+ *     // area is "10"
+ * }</pre>
  */
-
 public final class LargestRectangle {
+
     private LargestRectangle() {
     }
 
+    /**
+     * Calculates the largest rectangle area in the given histogram.
+     *
+     * @param heights an array of non-negative integers representing bar heights
+     * @return the largest rectangle area as a {@link String}
+     */
     public static String largestRectangleHistogram(int[] heights) {
-        int n = heights.length;
         int maxArea = 0;
-        Stack<int[]> st = new Stack<>();
-        for (int i = 0; i < n; i++) {
+        Stack<int[]> stack = new Stack<>();
+
+        for (int i = 0; i < heights.length; i++) {
             int start = i;
-            while (!st.isEmpty() && st.peek()[1] > heights[i]) {
-                int[] tmp = st.pop();
-                maxArea = Math.max(maxArea, tmp[1] * (i - tmp[0]));
-                start = tmp[0];
+            while (!stack.isEmpty() && stack.peek()[1] > heights[i]) {
+                int[] popped = stack.pop();
+                maxArea = Math.max(maxArea, popped[1] * (i - popped[0]));
+                start = popped[0];
             }
-            st.push(new int[] {start, heights[i]});
+            stack.push(new int[] {start, heights[i]});
         }
-        while (!st.isEmpty()) {
-            int[] tmp = st.pop();
-            maxArea = Math.max(maxArea, tmp[1] * (n - tmp[0]));
+
+        int totalLength = heights.length;
+        while (!stack.isEmpty()) {
+            int[] remaining = stack.pop();
+            maxArea = Math.max(maxArea, remaining[1] * (totalLength - remaining[0]));
         }
-        return Integer.toString(maxArea);
-    }
 
-    public static void main(String[] args) {
-        assert largestRectangleHistogram(new int[] {2, 1, 5, 6, 2, 3}).equals("10");
-        assert largestRectangleHistogram(new int[] {2, 4}).equals("4");
+        return Integer.toString(maxArea);
     }
 }

src/main/java/com/thealgorithms/strings/Isomorphic.java

@@ -5,35 +5,54 @@
 import java.util.Map;
 import java.util.Set;
 
+/**
+ * Utility class to check if two strings are isomorphic.
+ *
+ * <p>
+ * Two strings {@code s} and {@code t} are isomorphic if the characters in {@code s}
+ * can be replaced to get {@code t}, while preserving the order of characters.
+ * Each character must map to exactly one character, and no two characters can map to the same character.
+ * </p>
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Isomorphism_(computer_science)">Isomorphic Strings</a>
+ */
 public final class Isomorphic {
+
     private Isomorphic() {
     }
 
-    public static boolean checkStrings(String s, String t) {
+    /**
+     * Checks if two strings are isomorphic.
+     *
+     * @param s the first input string
+     * @param t the second input string
+     * @return {@code true} if {@code s} and {@code t} are isomorphic; {@code false} otherwise
+     */
+    public static boolean areIsomorphic(String s, String t) {
         if (s.length() != t.length()) {
             return false;
         }
 
-        // To mark the characters of string using MAP
-        // character of first string as KEY and another as VALUE
-        // now check occurence by keeping the track with SET data structure
-        Map<Character, Character> characterMap = new HashMap<>();
-        Set<Character> trackUniqueCharacter = new HashSet<>();
+        Map<Character, Character> map = new HashMap<>();
+        Set<Character> usedCharacters = new HashSet<>();
 
         for (int i = 0; i < s.length(); i++) {
-            if (characterMap.containsKey(s.charAt(i))) {
-                if (t.charAt(i) != characterMap.get(s.charAt(i))) {
+            char sourceChar = s.charAt(i);
+            char targetChar = t.charAt(i);
+
+            if (map.containsKey(sourceChar)) {
+                if (map.get(sourceChar) != targetChar) {
                     return false;
                 }
             } else {
-                if (trackUniqueCharacter.contains(t.charAt(i))) {
+                if (usedCharacters.contains(targetChar)) {
                     return false;
                 }
-
-                characterMap.put(s.charAt(i), t.charAt(i));
+                map.put(sourceChar, targetChar);
+                usedCharacters.add(targetChar);
             }
-            trackUniqueCharacter.add(t.charAt(i));
         }
+
         return true;
     }
 }

src/main/java/com/thealgorithms/strings/LongestCommonPrefix.java

@@ -2,21 +2,41 @@
 
 import java.util.Arrays;
 
+/**
+ * Utility class for string operations.
+ * <p>
+ * This class provides a method to find the longest common prefix (LCP)
+ * among an array of strings.
+ * </p>
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Longest_common_prefix">Longest Common Prefix - Wikipedia</a>
+ */
 public final class LongestCommonPrefix {
-    public String longestCommonPrefix(String[] strs) {
+
+    private LongestCommonPrefix() {
+    }
+
+    /**
+     * Finds the longest common prefix among a list of strings using lexicographical sorting.
+     * The prefix is common to the first and last elements after sorting the array.
+     *
+     * @param strs array of input strings
+     * @return the longest common prefix, or empty string if none exists
+     */
+    public static String longestCommonPrefix(String[] strs) {
         if (strs == null || strs.length == 0) {
             return "";
         }
 
         Arrays.sort(strs);
-        String shortest = strs[0];
-        String longest = strs[strs.length - 1];
+        String first = strs[0];
+        String last = strs[strs.length - 1];
 
         int index = 0;
-        while (index < shortest.length() && index < longest.length() && shortest.charAt(index) == longest.charAt(index)) {
+        while (index < first.length() && index < last.length() && first.charAt(index) == last.charAt(index)) {
             index++;
         }
 
-        return shortest.substring(0, index);
+        return first.substring(0, index);
     }
 }

src/test/java/com/thealgorithms/stacks/LargestRectangleTest.java

@@ -2,76 +2,27 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import org.junit.jupiter.api.Test;
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
 public class LargestRectangleTest {
 
-    @Test
-    void testLargestRectangleHistogramWithTypicalCases() {
-        // Typical case with mixed heights
-        int[] heights = {2, 1, 5, 6, 2, 3};
-        String expected = "10";
-        String result = LargestRectangle.largestRectangleHistogram(heights);
-        assertEquals(expected, result);
-
-        // Another typical case with increasing heights
-        heights = new int[] {2, 4};
-        expected = "4";
-        result = LargestRectangle.largestRectangleHistogram(heights);
-        assertEquals(expected, result);
-
-        // Case with multiple bars of the same height
-        heights = new int[] {4, 4, 4, 4};
-        expected = "16";
-        result = LargestRectangle.largestRectangleHistogram(heights);
-        assertEquals(expected, result);
+    @ParameterizedTest(name = "Histogram: {0} → Expected area: {1}")
+    @MethodSource("histogramProvider")
+    void testLargestRectangleHistogram(int[] heights, String expected) {
+        assertEquals(expected, LargestRectangle.largestRectangleHistogram(heights));
     }
 
-    @Test
-    void testLargestRectangleHistogramWithEdgeCases() {
-        // Edge case with an empty array
-        int[] heights = {};
-        String expected = "0";
-        String result = LargestRectangle.largestRectangleHistogram(heights);
-        assertEquals(expected, result);
-
-        // Edge case with a single bar
-        heights = new int[] {5};
-        expected = "5";
-        result = LargestRectangle.largestRectangleHistogram(heights);
-        assertEquals(expected, result);
-
-        // Edge case with all bars of height 0
-        heights = new int[] {0, 0, 0};
-        expected = "0";
-        result = LargestRectangle.largestRectangleHistogram(heights);
-        assertEquals(expected, result);
+    static Stream<Arguments> histogramProvider() {
+        return Stream.of(Arguments.of(new int[] {2, 1, 5, 6, 2, 3}, "10"), Arguments.of(new int[] {2, 4}, "4"), Arguments.of(new int[] {4, 4, 4, 4}, "16"), Arguments.of(new int[] {}, "0"), Arguments.of(new int[] {5}, "5"), Arguments.of(new int[] {0, 0, 0}, "0"),
+            Arguments.of(new int[] {6, 2, 5, 4, 5, 1, 6}, "12"), Arguments.of(new int[] {2, 1, 5, 6, 2, 3, 1}, "10"), Arguments.of(createLargeArray(10000, 1), "10000"));
     }
 
-    @Test
-    void testLargestRectangleHistogramWithLargeInput() {
-        // Large input case
-        int[] heights = new int[10000];
-        for (int i = 0; i < heights.length; i++) {
-            heights[i] = 1;
-        }
-        String expected = "10000";
-        String result = LargestRectangle.largestRectangleHistogram(heights);
-        assertEquals(expected, result);
-    }
-
-    @Test
-    void testLargestRectangleHistogramWithComplexCases() {
-        // Complex case with a mix of heights
-        int[] heights = {6, 2, 5, 4, 5, 1, 6};
-        String expected = "12";
-        String result = LargestRectangle.largestRectangleHistogram(heights);
-        assertEquals(expected, result);
-
-        // Case with a peak in the middle
-        heights = new int[] {2, 1, 5, 6, 2, 3, 1};
-        expected = "10";
-        result = LargestRectangle.largestRectangleHistogram(heights);
-        assertEquals(expected, result);
+    private static int[] createLargeArray(int size, int value) {
+        int[] arr = new int[size];
+        java.util.Arrays.fill(arr, value);
+        return arr;
     }
 }

src/test/java/com/thealgorithms/strings/IsomorphicTest.java

@@ -12,8 +12,8 @@ public final class IsomorphicTest {
     @ParameterizedTest
     @MethodSource("inputs")
     public void testCheckStrings(String str1, String str2, Boolean expected) {
-        assertEquals(expected, Isomorphic.checkStrings(str1, str2));
-        assertEquals(expected, Isomorphic.checkStrings(str2, str1));
+        assertEquals(expected, Isomorphic.areIsomorphic(str1, str2));
+        assertEquals(expected, Isomorphic.areIsomorphic(str2, str1));
     }
 
     private static Stream<Arguments> inputs() {

src/test/java/com/thealgorithms/strings/LongestCommonPrefixTest.java

@@ -2,72 +2,23 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import org.junit.jupiter.api.Test;
+import java.util.stream.Stream;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
 public class LongestCommonPrefixTest {
 
-    private final LongestCommonPrefix longestCommonPrefix = new LongestCommonPrefix();
-
-    @Test
-    public void testCommonPrefix() {
-        String[] input = {"flower", "flow", "flight"};
-        String expected = "fl";
-        assertEquals(expected, longestCommonPrefix.longestCommonPrefix(input));
-    }
-
-    @Test
-    public void testNoCommonPrefix() {
-        String[] input = {"dog", "racecar", "car"};
-        String expected = "";
-        assertEquals(expected, longestCommonPrefix.longestCommonPrefix(input));
-    }
-
-    @Test
-    public void testEmptyArray() {
-        String[] input = {};
-        String expected = "";
-        assertEquals(expected, longestCommonPrefix.longestCommonPrefix(input));
-    }
-
-    @Test
-    public void testNullArray() {
-        String[] input = null;
-        String expected = "";
-        assertEquals(expected, longestCommonPrefix.longestCommonPrefix(input));
-    }
-
-    @Test
-    public void testSingleString() {
-        String[] input = {"single"};
-        String expected = "single";
-        assertEquals(expected, longestCommonPrefix.longestCommonPrefix(input));
-    }
-
-    @Test
-    public void testCommonPrefixWithDifferentLengths() {
-        String[] input = {"ab", "a"};
-        String expected = "a";
-        assertEquals(expected, longestCommonPrefix.longestCommonPrefix(input));
-    }
-
-    @Test
-    public void testAllSameStrings() {
-        String[] input = {"test", "test", "test"};
-        String expected = "test";
-        assertEquals(expected, longestCommonPrefix.longestCommonPrefix(input));
-    }
-
-    @Test
-    public void testPrefixAtEnd() {
-        String[] input = {"abcde", "abcfgh", "abcmnop"};
-        String expected = "abc";
-        assertEquals(expected, longestCommonPrefix.longestCommonPrefix(input));
+    @ParameterizedTest(name = "{index} => input={0}, expected=\"{1}\"")
+    @MethodSource("provideTestCases")
+    @DisplayName("Test Longest Common Prefix")
+    void testLongestCommonPrefix(String[] input, String expected) {
+        assertEquals(expected, LongestCommonPrefix.longestCommonPrefix(input));
     }
 
-    @Test
-    public void testMixedCase() {
-        String[] input = {"Flower", "flow", "flight"};
-        String expected = "";
-        assertEquals(expected, longestCommonPrefix.longestCommonPrefix(input));
+    private static Stream<Arguments> provideTestCases() {
+        return Stream.of(Arguments.of(new String[] {"flower", "flow", "flight"}, "fl"), Arguments.of(new String[] {"dog", "racecar", "car"}, ""), Arguments.of(new String[] {}, ""), Arguments.of(null, ""), Arguments.of(new String[] {"single"}, "single"), Arguments.of(new String[] {"ab", "a"}, "a"),
+            Arguments.of(new String[] {"test", "test", "test"}, "test"), Arguments.of(new String[] {"abcde", "abcfgh", "abcmnop"}, "abc"), Arguments.of(new String[] {"Flower", "flow", "flight"}, ""));
     }
 }