solve: longest repeating character replacement

Author: sounmind

longest-repeating-character-replacement/evan.js

@@ -0,0 +1,45 @@
+/**
+ * @param {string} str
+ * @param {number} maxConvertCount
+ * @return {number}
+ */
+var characterReplacement = function (str, maxConvertCount) {
+  const freqInWindow = {};
+  let maxLength = 0;
+  let maxCharFreqInWindow = 0;
+  let leftIndex = 0;
+
+  for (let rightIndex = 0; rightIndex < str.length; rightIndex++) {
+    const slidingWindow = [str[leftIndex], str[rightIndex]];
+    const [leftChar, rightChar] = slidingWindow;
+
+    freqInWindow[rightChar] = (freqInWindow[rightChar] || 0) + 1;
+    maxCharFreqInWindow = Math.max(
+      maxCharFreqInWindow,
+      freqInWindow[rightChar]
+    );
+
+    // while (currentWindowLength > maxConvertCount + maxCharFreqInWindow) {
+    // while (cannot convert all characters in the window to the same character) {
+    while (rightIndex - leftIndex + 1 > maxConvertCount + maxCharFreqInWindow) {
+      leftIndex += 1;
+      freqInWindow[leftChar] -= 1;
+    }
+
+    maxLength = Math.max(maxLength, rightIndex - leftIndex + 1);
+  }
+
+  return maxLength;
+};
+
+/**
+ * Time Complexity: O(n)
+ * - The right pointer iterates through the string once, making it O(n).
+ * - The left pointer only moves when necessary, also contributing to O(n) overall.
+ * - Thus, the total time complexity is O(n).
+ *
+ * Space Complexity: O(1)
+ * - The frequency object stores counts for at most 26 letters in the English alphabet.
+ * - Since the space used by the frequency object is constant and does not scale with input size,
+ *   the space complexity is O(1).
+ */