LeetCode – Longest Substring with At Least K Repeating Characters (Java)
Find the length of the longest substring T of a given string (consists of lowercase letters only) such that every character in T appears no less than k times.
Example 1:
Input: s = "aaabb", k = 3 Output: 3 The longest substring is "aaa", as 'a' is repeated 3 times.
Java Solution
public int longestSubstring(String s, int k) { HashMap<Character, Integer> counter = new HashMap<Character, Integer>(); for(int i=0; i<s.length(); i++){ char c = s.charAt(i); if(counter.containsKey(c)){ counter.put(c, counter.get(c)+1); }else{ counter.put(c, 1); } } HashSet<Character> splitSet = new HashSet<Character>(); for(char c: counter.keySet()){ if(counter.get(c)<k){ splitSet.add(c); } } if(splitSet.isEmpty()){ return s.length(); } int max = 0; int i=0, j=0; while(j<s.length()){ char c = s.charAt(j); if(splitSet.contains(c)){ if(j!=i){ max = Math.max(max, longestSubstring(s.substring(i, j), k)); } i=j+1; } j++; } if(i!=j) max = Math.max(max, longestSubstring(s.substring(i, j), k)); return max; } 
<pre><code> String foo = "bar"; </code></pre>

Sravan Deepala