2. Longest Repeating Character Replacement

Author: Sunjae95

longest-repeating-character-replacement/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * 1. brute force -> time limited
+ * 2. recursion -> failed to implement
+ * 3. dynamic programming -> failed to implement
+ * 4. dale solution https://www.algodale.com/problems/longest-repeating-character-replacement/
+ * n: length of list1 + list2
+ * time complexity: O(n^3)
+ * space complexity: O(n)
+ */
+
+/**
+ * brute force
+ * time complexity: O(n^3)
+ * space complexity: O(n)
+ */
+// var characterReplacement = function (s, k) {
+//   let answer = 0;
+//   const set = new Set();
+//   for (let i = 0; i < s.length; i++) set.add(s[i]);
+//   for (let i = 0; i < s.length; i++) {
+//     for (const now of set) {
+//       let current = 0;
+//       let count = k;
+
+//       for (let j = i; j < s.length; j++) {
+//         if (now === s[j]) current++;
+//         else if (count) {
+//           current++;
+//           count--;
+//         }
+//         break;
+//       }
+//       answer = Math.max(answer, current);
+//     }
+//   }
+
+//   return answer;
+// };
+
+/**
+ * time complexity: O(n)
+ * space complexity: O(1)
+ */
+var characterReplacement = function (s, k) {
+  let start = 0;
+  let answer = 0;
+
+  const map = new Map();
+  for (let i = 0; i < s.length; i++) map.set(s[i], 0);
+
+  for (let end = 0; end < s.length; end++) {
+    map.set(s[end], map.get(s[end]) + 1);
+    const maxLength = Math.max(...map.values());
+
+    while (end - start + 1 - maxLength > k) {
+      map.set(s[start], map.get(s[start]) - 1);
+      start++;
+    }
+
+    answer = Math.max(end - start + 1, answer);
+  }
+
+  return answer;
+};