Longest repeating character replacement

Author: nikoo28

src/main/java/leetcode/medium/LongestRepeatingCharacterReplacement.java

@@ -0,0 +1,37 @@
+package leetcode.medium;
+
+public class LongestRepeatingCharacterReplacement {
+
+  int characterReplacement(String s, int k) {
+
+    int[] freq = new int[26];
+    int left = 0;
+    int maxFreq = 0;
+    int maxWindow = 0;
+
+    for (int right = 0; right < s.length(); right++) {
+
+      // Update the frequency of the current character
+      freq[s.charAt(right) - 'A']++;
+
+      // Update the max frequency
+      maxFreq = Math.max(maxFreq, freq[s.charAt(right) - 'A']);
+
+      int windowLength = right - left + 1;
+
+      // If the windowLength - max frequency > k,
+      // then we need to shrink the window
+      if (windowLength - maxFreq > k) {
+        freq[s.charAt(left) - 'A']--;
+        left++;
+      }
+
+      windowLength = right - left + 1;
+      maxWindow = Math.max(maxWindow, windowLength);
+    }
+
+    return maxWindow;
+
+  }
+
+}

src/test/java/leetcode/medium/LongestRepeatingCharacterReplacementTest.java

@@ -0,0 +1,34 @@
+package leetcode.medium;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class LongestRepeatingCharacterReplacementTest {
+
+  private final LongestRepeatingCharacterReplacement longestRepeatingCharacterReplacement;
+
+  LongestRepeatingCharacterReplacementTest() {
+    longestRepeatingCharacterReplacement = new LongestRepeatingCharacterReplacement();
+  }
+
+  @Test
+  void testCharacterReplacement1() {
+    assertEquals(4, longestRepeatingCharacterReplacement.characterReplacement("ABAB", 2));
+  }
+
+  @Test
+  void testCharacterReplacement2() {
+    assertEquals(4, longestRepeatingCharacterReplacement.characterReplacement("AABABBA", 1));
+  }
+
+  @Test
+  void testCharacterReplacement3() {
+    assertEquals(2, longestRepeatingCharacterReplacement.characterReplacement("AABABBA", 0));
+  }
+
+  @Test
+  void testCharacterReplacement4() {
+    assertEquals(6, longestRepeatingCharacterReplacement.characterReplacement("AABABCCBCCB", 2));
+  }
+}