If the problem talks about continuous subarrays or substrings, the sliding window technique may help solve it in a linear time. Such problems are tricky, though the solution is simple once you get it. No wonder I am seeing such problems in almost every interview!
Here, we will take a look at Subarrays with K Different Integers (LeetCode Hard), which appeared on LeetCode weekly contest #123. You can also master the sliding windows technique with these additional problems:
- Longest Substring Without Repeating Characters
- Longest Substring with At Most Two Distinct Characters
- Longest Substring with At Most K Distinct Characters
Problem Description
Given an array
A of positive integers, call a (contiguous, not necessarily distinct) subarray of A good if the number of different integers in that subarray is exactly K. For example, [1,2,3,1,2] has 3 different integers: 1, 2, and 3.
Return the number of good subarrays of
A.Example
Input: A = [1,2,1,2,3], K = 2
Output: 7
Explanation: Subarrays formed with exactly 2 different integers: [1,2], [2,1], [1,2], [2,3], [1,2,1], [2,1,2], [1,2,1,2].
Output: 7
Explanation: Subarrays formed with exactly 2 different integers: [1,2], [2,1], [1,2], [2,3], [1,2,1], [2,1,2], [1,2,1,2].
