LeetCode Longest Substring With At Most K Distinct Characters

Author: pertrai1

0340-longest-substring-with-at-most-k-distinct-characters/README.md

@@ -328,6 +328,7 @@ A comprehensive collection of coding challenges from multiple platforms for lear
 - [0003 - Longest Substring Without Repeating Characters](./leetcode/medium/0003-longest-substring-without-repeating-characters) - Medium
 - [0159 - Longest Substring with At Most Two Distinct Characters](./leetcode/medium/0159-longest-substring-with-at-most-two-distinct-characters) - Medium
 - [0209 - Minimum Size Subarray Sum](./leetcode/medium/0209-minimum-size-subarray-sum) - Medium
+- [0340 - Longest Substring with At Most K Distinct Characters](./leetcode/medium/0340-longest-substring-with-at-most-k-distinct-characters) - Medium
 - [More in docs →](./docs/techniques/SLIDING_WINDOW.md)
 
 ### Hash Table / Hash Map

0340-longest-substring-with-at-most-k-distinct-characters/longest-substring-with-at-most-k-distinct-characters.ts

@@ -1,30 +1,24 @@
+# [Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters) ![Medium](https://img.shields.io/badge/Medium-orange)
 
-# [Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters) ![](https://img.shields.io/badge/Medium-orange)
+Given a string `s` and an integer `k`, return _the length of the longest **substring** of_ `s` _that contains at most_ `k` _**distinct** characters_.
 
-<p>Given a string <code>s</code> and an integer <code>k</code>, return <em>the length of the longest </em><span data-keyword="substring-nonempty"><em>substring</em></span><em> of</em> <code>s</code> <em>that contains at most</em> <code>k</code> <em><strong>distinct</strong> characters</em>.</p>
+## Example 1
 
-<p>&nbsp;</p>
-<p><strong class="example">Example 1:</strong></p>
+```text
+Input: s = "eceba", k = 2
+Output: 3
+Explanation: The substring is "ece" with length 3.
+```
 
-<pre>
-<strong>Input:</strong> s = &quot;eceba&quot;, k = 2
-<strong>Output:</strong> 3
-<strong>Explanation:</strong> The substring is &quot;ece&quot; with length 3.</pre>
+## Example 2
 
-<p><strong class="example">Example 2:</strong></p>
+```text
+Input: s = "aa", k = 1
+Output: 2
+Explanation: The substring is "aa" with length 2.
+```
 
-<pre>
-<strong>Input:</strong> s = &quot;aa&quot;, k = 1
-<strong>Output:</strong> 2
-<strong>Explanation:</strong> The substring is &quot;aa&quot; with length 2.
-</pre>
+## Constraints
 
-<p>&nbsp;</p>
-<p><strong>Constraints:</strong></p>
-
-<ul>
-	<li><code>1 &lt;= s.length &lt;= 5 * 10<sup>4</sup></code></li>
-	<li><code>0 &lt;= k &lt;= 50</code></li>
-</ul>
-
-        
+- `1 <= s.length <= 5 * 10^4`
+- `0 <= k <= 50`

README.md

@@ -1,25 +1,36 @@
-function lengthOfLongestSubstringKDistinct(s: string, k: number): number {
-    if (k === 0) return 0;
+/**
+ * @time - O(n) where n is the length of s
+ *          (each character visited at most twice by sliding window pointers)
+ * @space - O(k) where k is the maximum number of distinct characters allowed;
+ *          the map stores at most k + 1 characters at any time before shrinking
+ */
+export function lengthOfLongestSubstringKDistinct(s: string, k: number): number {
+  if (k === 0) return 0;
 
-    const characterCount = new Map<string, number>();
-    let left = 0;
-    let maxLength = 0;
+  const characterCount = new Map<string, number>();
+  let left = 0;
+  let maxLength = 0;
 
-    for (let right = 0; right < s.length; right++) {
-        const char = s[right];
-        characterCount.set(char, (characterCount.get(char) || 0) + 1);
+  // Expand the window by moving the right pointer
+  for (let right = 0; right < s.length; right++) {
+    const char = s[right];
+    // Add current character to frequency map
+    characterCount.set(char, (characterCount.get(char) || 0) + 1);
 
-        while (characterCount.size > k) {
-            const leftChar = s[left];
-            characterCount.set(leftChar, characterCount.get(leftChar)! - 1);
-            if (characterCount.get(leftChar) === 0) {
-                characterCount.delete(leftChar);
-            }
-            left++;
-        }
-
-        maxLength = Math.max(maxLength, right - left + 1);
+    // Shrink the window from the left if we have more than k distinct characters
+    while (characterCount.size > k) {
+      const leftChar = s[left];
+      characterCount.set(leftChar, characterCount.get(leftChar)! - 1);
+      // Remove the character from the map if its count drops to zero
+      if (characterCount.get(leftChar) === 0) {
+        characterCount.delete(leftChar);
+      }
+      left++;
     }
 
-    return maxLength;
-};
+    // Update the maximum length found so far
+    maxLength = Math.max(maxLength, right - left + 1);
+  }
+
+  return maxLength;
+}