Add Minimum Window Substring algorithm in Sliding Window package

src/main/java/com/thealgorithms/slidingwindow/MinimumWindowSubstring.java

@@ -0,0 +1,69 @@
+package com.thealgorithms.slidingwindow;
+
+import java.util.HashMap;
+
+/**
+ * Finds the minimum window substring in 's' that contains all characters of 't'.
+ *
+ * Worst-case performance O(n)
+ * Best-case performance O(n)
+ * Average performance O(n)
+ * Worst-case space complexity O(1)
+ *
+ * @author https://github.com/Chiefpatwal
+ */
+public final class MinimumWindowSubstring {
+    // Prevent instantiation
+    private MinimumWindowSubstring() {
+    }
+
+    /**
+     * Finds the minimum window substring of 's' containing all characters of 't'.
+     *
+     * @param s The input string to search within.
+     * @param t The string with required characters.
+     * @return The minimum window substring, or empty string if not found.
+     */
+    public static String minWindow(String s, String t) {
+        if (s.length() < t.length()) {
+            return "";
+        }
+
+        HashMap<Character, Integer> tFreq = new HashMap<>();
+        for (char c : t.toCharArray()) {
+            tFreq.put(c, tFreq.getOrDefault(c, 0) + 1);
+        }
+
+        HashMap<Character, Integer> windowFreq = new HashMap<>();
+        int left = 0;
+        int right = 0;
+        int minLen = Integer.MAX_VALUE;
+        int count = 0;
+        String result = "";
+
+        while (right < s.length()) {
+            char c = s.charAt(right);
+            windowFreq.put(c, windowFreq.getOrDefault(c, 0) + 1);
+
+            if (tFreq.containsKey(c) && windowFreq.get(c).intValue() <= tFreq.get(c).intValue()) {
+                count++;
+            }
+
+            while (count == t.length()) {
+                if (right - left + 1 < minLen) {
+                    minLen = right - left + 1;
+                    result = s.substring(left, right + 1);
+                }
+
+                char leftChar = s.charAt(left);
+                windowFreq.put(leftChar, windowFreq.get(leftChar) - 1);
+                if (tFreq.containsKey(leftChar) && windowFreq.get(leftChar) < tFreq.get(leftChar)) {
+                    count--;
+                }
+                left++;
+            }
+            right++;
+        }
+        return result;
+    }
+}

src/test/java/com/thealgorithms/slidingwindow/MinimumWindowSubstringTest.java

@@ -0,0 +1,35 @@
+package com.thealgorithms.slidingwindow;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Finds the minimum window substring in {@code s} that contains all characters of {@code t}.
+ *
+ * @param s The input string to search within
+ * @param t The string with required characters
+ * @return The minimum window substring, or empty string if not found
+ * @author  (https://github.com/Chiefpatwal)
+ */
+public class MinimumWindowSubstringTest {
+
+    /**
+     * Tests for MinimumWindowSubstring.minWindow.
+     */
+    @Test
+    public void testMinimumWindowSubstring() {
+        assertEquals("BANC", MinimumWindowSubstring.minWindow("ADOBECODEBANC", "ABC"));
+        assertEquals("a", MinimumWindowSubstring.minWindow("a", "a"));
+        assertEquals("", MinimumWindowSubstring.minWindow("a", "aa"));
+        assertEquals("", MinimumWindowSubstring.minWindow("ADOBECODEBANC", "XYZ"));
+        assertEquals("BC", MinimumWindowSubstring.minWindow("ABCDEF", "BC"));
+        assertEquals("q", MinimumWindowSubstring.minWindow("abcdefghijklmnopqrstuvwxyz", "q"));
+        assertEquals("", MinimumWindowSubstring.minWindow("zzzzzzzzz", "zzzzzzzzzz"));
+        assertEquals("abbbbbcdd", MinimumWindowSubstring.minWindow("aaaaaaaaaaaabbbbbcdd", "abcdd"));
+        assertEquals("ABCDEFG", MinimumWindowSubstring.minWindow("ABCDEFG", "ABCDEFG"));
+        assertEquals("", MinimumWindowSubstring.minWindow("abc", "A"));
+        assertEquals("A", MinimumWindowSubstring.minWindow("aAbBcC", "A"));
+        assertEquals("AABBC", MinimumWindowSubstring.minWindow("AAABBC", "AABC"));
+    }
+}