Implement characterReplacement method in Java

03. Sliding Window/03.LongestRepeatingCharacterReplacement.md

@@ -63,3 +63,27 @@ class Solution {
     }
 }
 ```
+
+```java
+class Solution {
+    public int characterReplacement(String s, int k) {
+        int[] freqArray=new int[26]; // Storing Frequency of characters A-Z
+        int left=0, maxFreq=0,longestSubstring=0;
+        for(int right=0;right<s.length();right++){ //expanding right 
+            char ch=s.charAt(right);//take curr char
+            freqArray[ch-'A']++;//inc the freq of char in array
+            maxFreq=Math.max(maxFreq,freqArray[ch-'A']);//cal max freq acc to curr char 
+             // Characters needed to replace = windowSize - maxFreq
+             //and if replace >k then we shrink win until it becomes valid agn 
+            while((right-left+1)-maxFreq>k){
+                freqArray[s.charAt(left)-'A']--;// Remove left character from window
+                left++;
+            } 
+            //cal longest substing length
+            longestSubstring=Math.max(right-left+1,longestSubstring);
+        }
+        return longestSubstring;
+
+    }
+}
+```