add LongestSubstringWithAtMostKDistinctCharacters, ReconstructItinerary, LargestBstSubtree

Author: FreeTymeKiyan

src/main/java/com/freetymekiyan/algorithms/level/hard/LongestSubstringWithAtMostKDistinctCharacters.java

@@ -0,0 +1,100 @@
+package com.freetymekiyan.algorithms.level.hard;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+/**
+ * 340. Longest Substring with At Most K Distinct Characters
+ * <p>
+ * Given a string, find the length of the longest substring T that contains at most k distinct characters.
+ * <p>
+ * Example 1:
+ * <p>
+ * Input: s = "eceba", k = 2
+ * Output: 3
+ * Explanation: T is "ece" which its length is 3.
+ * Example 2:
+ * <p>
+ * Input: s = "aa", k = 1
+ * Output: 2
+ * Explanation: T is "aa" which its length is 2.
+ * <p>
+ * Companies: Facebook, Amazon, Google, Bloomberg, AppDynamics, Coupang
+ * <p>
+ * Related Topics: Hash Table, String, Sliding Window
+ * <p>
+ * Similar Questions: (M) Longest Substring Without Repeating Characters, (H) Longest Substring with At Most Two
+ * Distinct Characters, (M) Longest Repeating Character Replacement, (H) Subarrays with K Different Integers, (M) Max
+ * Consecutive Ones III
+ */
+public class LongestSubstringWithAtMostKDistinctCharacters {
+
+  public int lengthOfLongestSubstringKDistinct(String s, int k) {
+    int n = s.length();
+    if (n * k == 0) return 0;
+
+    // sliding window left and right pointers
+    int left = 0;
+    int right = 0;
+    // hashmap character -> its rightmost position
+    // in the sliding window
+    LinkedHashMap<Character, Integer> hashmap = new LinkedHashMap<>(k + 1);
+
+    int maxLength = 1;
+
+    while (right < n) {
+      Character character = s.charAt(right);
+      // if character is already in the hashmap -
+      // delete it, so that after insert it becomes
+      // the rightmost element in the hashmap
+      if (hashmap.containsKey(character))
+        hashmap.remove(character);
+      hashmap.put(character, right++);
+
+      // slidewindow contains k + 1 characters
+      if (hashmap.size() == k + 1) {
+        // delete the leftmost character
+        Map.Entry<Character, Integer> leftmost = hashmap.entrySet().iterator().next();
+        hashmap.remove(leftmost.getKey());
+        // move left pointer of the slidewindow
+        left = leftmost.getValue() + 1;
+      }
+
+      maxLength = Math.max(maxLength, right - left);
+    }
+    return maxLength;
+  }
+
+  public int lengthOfLongestSubstringKDistinct2(String s, int k) {
+    int n = s.length();
+    if (n * k == 0) return 0;
+
+    // sliding window left and right pointers
+    int left = 0;
+    int right = 0;
+    // hashmap character -> its rightmost position
+    // in the sliding window
+    Map<Character, Integer> hashmap = new HashMap<Character, Integer>();
+
+    int maxLength = 1;
+
+    while (right < n) {
+      // add new character and move right pointer
+      hashmap.put(s.charAt(right), right++);
+
+      // slidewindow contains 3 characters
+      if (hashmap.size() == k + 1) {
+        // delete the leftmost character
+        int del_idx = Collections.min(hashmap.values());
+        hashmap.remove(s.charAt(del_idx));
+        // move left pointer of the slidewindow
+        left = del_idx + 1;
+      }
+
+      maxLength = Math.max(maxLength, right - left);
+    }
+    return maxLength;
+  }
+}