Feat: 424. Longest Repeating Character Replacement

Author: HC-kang

longest-repeating-character-replacement/HC-kang.ts

@@ -0,0 +1,25 @@
+/**
+ * https://leetcode.com/problems/longest-repeating-character-replacement
+ * T.C. O(n)
+ * S.C. O(1)
+ */
+function characterReplacement(s: string, k: number): number {
+  const charCount = new Array(26).fill(0);
+  let maxCount = 0;
+  let start = 0;
+  let maxLen = 0;
+
+  const A = 'A'.charCodeAt(0);
+  for (let end = 0; end < s.length; end++) {
+    const endCharIdx = s.charCodeAt(end) - A;
+    maxCount = Math.max(maxCount, ++charCount[endCharIdx]);
+
+    if (end - start + 1 - maxCount > k) {
+      charCount[s.charCodeAt(start) - A]--;
+      start++;
+    }
+
+    maxLen = Math.max(maxLen, end - start + 1);
+  }
+  return maxLen;
+}