Longest Repeating Character Replacement

longest-repeating-character-replacement/TonyKim9401.java

@@ -0,0 +1,27 @@
+// TC: O(26 * n) => O(n)
+// iterates 26 times at the first for-loop, while loop O(n)
+// SC: O(1)
+class Solution {
+    public int characterReplacement(String s, int k) {
+        int ans = 0;
+        int n = s.length();
+        for (char c = 'A'; c <= 'Z'; c++) {
+            int i = 0, j = 0, replaced = 0;
+            while (j < n) {
+                if (s.charAt(j) == c) {
+                    j += 1;
+                } else if (replaced < k) {
+                    j += 1;
+                    replaced++;
+                } else if (s.charAt(i) == c) {
+                    i += 1;
+                } else {
+                    i += 1;
+                    replaced -= 1;
+                }
+                ans = Math.max(ans, j - i);
+            }
+        }
+        return ans;
+    }
+}