You are given the string croakOfFrogs, which represents a combination of the string "croak" from different frogs, that is, multiple frogs can croak at the same time, so multiple "croak" are mixed.
Return the minimum number of different frogs to finish all the croaks in the given string.
A valid "croak" means a frog is printing five letters 'c', 'r', 'o', 'a', and 'k' sequentially. The frogs have to print all five letters to finish a croak. If the given string is not a combination of a valid "croak" return -1.
Example 1:
Input: croakOfFrogs = "croakcroak" Output: 1 Explanation: One frog yelling "croak" twice.
Example 2:
Input: croakOfFrogs = "crcoakroak" Output: 2 Explanation: The minimum number of frogs is two. The first frog could yell "crcoakroak". The second frog could yell later "crcoakroak".
Example 3:
Input: croakOfFrogs = "croakcrook" Output: -1 Explanation: The given string is an invalid combination of "croak" from different frogs.
Constraints:
1 <= croakOfFrogs.length <= 105croakOfFrogs is either 'c', 'r', 'o', 'a', or 'k'.In #1419 Minimum Number of Frogs Croaking, the goal is to determine the smallest number of frogs needed to produce a given sequence representing overlapping croaks of the word "croak". Since each frog must croak in the exact order of characters, the key idea is to track how many frogs are currently at each stage of the croak.
A common strategy is to use counting or frequency tracking for each character in the sequence (c → r → o → a → k). As you iterate through the string, update counts to ensure the order remains valid. Whenever a new c appears without a completed frog available, it indicates a new frog starting its croak. When k is reached, that frog becomes available again.
The maximum number of frogs simultaneously croaking during the scan represents the final answer. Careful validation ensures the sequence is valid. This approach runs in O(n) time with O(1) extra space.
| Approach | Time Complexity | Space Complexity |
|---|---|---|
| Counting characters across croak stages | O(n) | O(1) |
Natural Habitat Shorts
Use these hints if you're stuck. Try solving on your own first.
keep the frequency of all characters from "croak" using a hashmap.
For each character in the given string, greedily match it to a possible "croak".
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Each frog must croak in the exact order of the letters c, r, o, a, k. Tracking stages ensures that the sequence is valid and that characters appear in the correct progression. It also helps determine when a frog finishes a croak and can be reused.
Yes, variations of this problem can appear in technical interviews because it tests string processing, counting techniques, and state tracking. It is especially useful for evaluating a candidate's ability to model sequential processes efficiently.
A simple array or set of counters works best because there are only five characters in the sequence "croak". These counters track how many frogs are currently at each stage. This keeps the space complexity constant and the implementation efficient.
The optimal approach uses a counting technique to track how many frogs are at each stage of the word "croak". By scanning the string once and updating stage counts, you can determine how many frogs are croaking simultaneously. The maximum concurrent frogs during the scan gives the minimum number required.