Construct String With Repeat Limit

Construct String With Repeat Limit - Problem

You are given a string s and an integer repeatLimit. Construct a new string repeatLimitedString using the characters of s such that no letter appears more than repeatLimit times in a row.

You do not have to use all characters from s.

Return the lexicographically largest repeatLimitedString possible.

A string a is lexicographically larger than a string b if in the first position where a and b differ, string a has a letter that appears later in the alphabet than the corresponding letter in b. If the first min(a.length, b.length) characters do not differ, then the longer string is the lexicographically larger one.

Input & Output

Example 1 — Basic Case

$ Input: s = "cczazcc", repeatLimit = 3

› Output: "zzcccacc"

💡 Note: Start with largest character 'z' (appears 2 times), then 'c' (3 times max), then use 'a' as separator, then remaining 'c'.

Example 2 — Repeat Limit Hit

$ Input: s = "aababab", repeatLimit = 2

› Output: "bbabaa"

💡 Note: Use 'b' twice, then 'a' as separator, then 'b' once, then remaining 'a' characters.

Example 3 — Single Character Type

$ Input: s = "aaaa", repeatLimit = 2

› Output: "aa"

💡 Note: Only one character type available, use up to repeat limit and stop (no separator available).

Constraints

1 ≤ s.length ≤ 10⁵
1 ≤ repeatLimit ≤ 10⁴
s consists of lowercase English letters.

Visualization

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Asked in

G Google 28 a Amazon 23 f Facebook 15 M Microsoft 12

The key insight is to greedily use the largest available character while respecting the repeat limit, using the next largest as separator when needed. Best approach uses frequency counting with greedy construction for optimal performance. Time: O(n), Space: O(1).

Common Approaches

✓ Two Pointers

⏱️ Time: N/A Space: N/A

Brute Force - Generate All Permutations

⏱️ Time: O(n!) Space: O(n!)

Generate every possible arrangement of characters from the input string, check if each arrangement satisfies the repeat limit constraint, and return the lexicographically largest valid arrangement.

Frequency Count + Greedy Construction

⏱️ Time: O(n) Space: O(1)

Count the frequency of each character, then greedily construct the result by always choosing the largest available character while respecting the repeat limit constraint.

Max Heap Priority Queue

⏱️ Time: O(n + k log k) Space: O(k)

Use a max heap (priority queue) to maintain characters by their lexicographical order. Always extract the largest character and use it up to the repeat limit, then use the second largest as separator when needed.

Algorithm Steps — Algorithm Steps

Code -

solution.c — C

Time & Space Complexity

Time Complexity

⏱️

✓ Linear Growth

Space Complexity

✓ Linear Space

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Medium-High Frequency

~25 min Avg. Time

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Smart Actions

💡 Explanation

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