Substring or Subarray Search

Sliding Window Algorithm

Sliding Window algorithm template to solve all the Leetcode substring search problem.

Problems could be solved with sliding window algorithm:

Longest Substring with At Most Two Distinct Characters

Longest Substring with At Most K Distinct Characters

Fruit into baskets

Example: Longest Substring with At Most K Distinct Characters

class Solution {
    public int lengthOfLongestSubstringKDistinct(String s, int k) {
        if (s == null || s.length() == 0 || k == 0) {
            return 0;
        }
        HashMap<Character, Integer> count = new HashMap<>();
        int n = s.length();
        int firstIdx = 0;
        char[] chs = s.toCharArray();

        int longest = 0;

        for (int i = 0; i < n; i++) {
            count.put(chs[i], count.getOrDefault(chs[i], 0) + 1);
            while (count.size() > k) {
                count.put(chs[firstIdx], count.get(chs[firstIdx]) - 1);
                if (count.get(chs[firstIdx]) == 0) {
                    count.remove(chs[firstIdx]);
                }
                firstIdx++;
            }
            longest = Math.max(longest, i - firstIdx + 1);
        }
        return longest;
    }
}