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Problem solution · Java

Count of Substrings Containing Every Vowel and K Consonants I

Count of Substrings Containing Every Vowel and K Consonants I: a Java solution using sliding window or two pointers. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Sliding window or two pointers
Source
walkccc LeetCode Solutions
Length
52 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Sliding window or two pointers

For Count of Substrings Containing Every Vowel and K Consonants I, the implementation maintains a moving interval and updates only the information that enters or leaves the window.

  1. Choose the invariant that makes a window valid or useful.
  2. Advance the right boundary and add the new element.
  3. Move the left boundary only as needed while maintaining the invariant and updating the answer.

Code notes

  • 52 lines of Java from the credited upstream file 3305.java.
  • The implementation visibly relies on hash lookup, ordered lookup.
  • 2 loop blocks detected.

Complexity

Confirm that neither pointer moves backwards; if so, the scan is usually linear apart from the window’s data-structure operations.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeCount of Substrings Containing Every Vowel and K Consonants I · JavaJava
Use this to learn the idea, then write your own version.
class Solution {  public int countOfSubstrings(String word, int k) {    return substringsWithAtMost(word, k) - substringsWithAtMost(word, k - 1);  }   // Return the number of substrings containing every vowel with at most k  // consonants.  private int substringsWithAtMost(String word, int k) {    if (k == -1)      return 0;     int res = 0;    int vowels = 0;    int uniqueVowels = 0;    Map<Character, Integer> vowelLastSeen = new HashMap<>();     for (int l = 0, r = 0; r < word.length(); ++r) {      if (isVowel(word.charAt(r))) {        ++vowels;        if (!vowelLastSeen.containsKey(word.charAt(r)) || vowelLastSeen.get(word.charAt(r)) < l)          ++uniqueVowels;        vowelLastSeen.put(word.charAt(r), r);      }      while (r - l + 1 - vowels > k) {        if (isVowel(word.charAt(l))) {          --vowels;          if (vowelLastSeen.get(word.charAt(l)) == l)            --uniqueVowels;        }        ++l;      }      if (uniqueVowels == 5) {        // Add substrings containing every vowel with at most k consonants to        // the answer. They are        // word[l..r], word[l + 1..r], ..., word[min(vowelLastSeen[vowel])..r]        final int minVowelLastSeen = Arrays.asList('a', 'e', 'i', 'o', 'u')                                         .stream()                                         .mapToInt(vowel -> vowelLastSeen.get(vowel))                                         .min()                                         .getAsInt();        res += minVowelLastSeen - l + 1;      }    }     return res;  }   private boolean isVowel(char c) {    return "aeiou".indexOf(c) != -1;  }}

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