Is Take K of Each Character From Left and Right easy or hard?

The problem is rated Medium because the greedy insight is not immediately obvious. Many candidates initially simulate removing characters from both ends. Recognizing that the problem can be reframed as keeping the longest valid middle substring leads to the optimal O(n) sliding window solution.

Take K of Each Character From Left and Right Python/Java solution

Python, Java, C++, and JavaScript implementations typically use the same sliding window logic. Maintain two pointers and update frequency counts as the window expands or shrinks. The result is computed as n minus the longest valid window length.

How to solve Take K of Each Character From Left and Right in O(n)?

First compute the total count of each character. Then determine how many of each character can remain in the middle substring: total[c] - k. Use a sliding window to find the longest substring that does not exceed these limits. The minimum minutes equals n minus the length of that window.

What is the best approach for Take K of Each Character From Left and Right?

The sliding window complement approach is considered the best solution. Instead of deciding which characters to remove from the ends, you find the longest middle substring that can remain while still leaving at least k of each character outside it. This transforms the problem into a standard sliding window scan with O(n) time and O(1) space.

Is Take K of Each Character From Left and Right asked at Google/Amazon/Meta?

This problem matches the pattern of sliding window and two-pointer interview questions commonly used by companies like Google, Amazon, and Meta. Variations of "take from ends" or "longest valid substring under constraints" appear frequently in coding interviews.

What data structure is used in Take K of Each Character From Left and Right?

The solution mainly uses counters or a small hash table to track the frequency of characters inside the sliding window. Since the string only contains 'a', 'b', and 'c', many implementations use a fixed-size array of length three for constant-time updates.

What is the time complexity of Take K of Each Character From Left and Right?

The optimal solution runs in O(n) time where n is the length of the string. Each character is processed at most twice by the sliding window pointers. Space complexity is O(1) because only a few counters for 'a', 'b', and 'c' are maintained.

Description Hints 3 Solution Video 17:19

2516. Take K of Each Character From Left and Right

Medium51.4% acceptance3 companies

You are given a string s consisting of the characters 'a', 'b', and 'c' and a non-negative integer k. Each minute, you may take either the leftmost character of s, or the rightmost character of s.

Return the minimum number of minutes needed for you to take at least k of each character, or return -1 if it is not possible to take k of each character.

Example 1:

Input: s = "aabaaaacaabc", k = 2
Output: 8
Explanation: 
Take three characters from the left of s. You now have two 'a' characters, and one 'b' character.
Take five characters from the right of s. You now have four 'a' characters, two 'b' characters, and two 'c' characters.
A total of 3 + 5 = 8 minutes is needed.
It can be proven that 8 is the minimum number of minutes needed.

Example 2:

Input: s = "a", k = 1
Output: -1
Explanation: It is not possible to take one 'b' or 'c' so return -1.

Constraints:

1 <= s.length <= 10⁵
s consists of only the letters 'a', 'b', and 'c'.
0 <= k <= s.length

Asked at 3 companies

Google Amazon Bloomberg

Topics

Hints open one at a time

Hint 1

Start by counting the frequency of each character and checking if it is possible.

Hint 2

If you take x characters from the left side, what is the minimum number of characters you need to take from the right side? Find this for all values of x in the range 0 ≤ x ≤ s.length.

Hint 3

Use a two-pointers approach to avoid computing the same information multiple times.

17:19

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