add: LongestUniformSubstringAfterReplacements

Author: Jer3myYu

java/Sliding Windows/LongestUniformSubstringAfterReplacements.java

@@ -0,0 +1,35 @@
+import java.util.HashMap;
+import java.util.Map;
+
+public class LongestUniformSubstringAfterReplacements {
+    public int longestUniformSubstringAfterReplacements(String s, int k) {
+        Map<Character, Integer> freqs = new HashMap<>();
+        int highestFreq = 0;
+        int maxLen = 0;
+        int left, right;
+        left = right = 0;
+        while (right < s.length()) {
+            // Update the frequency of the character at the right pointer 
+            // and the highest frequency for the current window.
+            freqs.put(s.charAt(right), freqs.getOrDefault(s.charAt(right), 0) + 1);
+            highestFreq = Math.max(highestFreq, freqs.get(s.charAt(right)));
+            // Calculate replacements needed for the current window.
+            int numCharsToReplace = (right - left + 1) - highestFreq;
+            // Slide the window if the number of replacements needed exceeds 
+            // 'k'. The right pointer always gets advanced, so we just need 
+            // to advance 'left'.
+            if (numCharsToReplace > k) {
+                // Remove the character at the left pointer from the hash map 
+                // before advancing the left pointer.
+                freqs.put(s.charAt(left), freqs.get(s.charAt(left)) - 1);
+                left++;
+            }
+            // Since the length of the current window increases or stays the 
+            // same, assign  the length of the current window to 'maxLen'.
+            maxLen = right - left + 1;
+            // Expand the window.
+            right++;
+        }
+        return maxLen;
+    }
+}