949. largest time for given digits is a combinatorial challenge that asks you to build the latest valid clock time using a fixed set of four digits. The task forces you to explore every permutation, validate hour and minute ranges, and return the largest time in HH:MM format or an empty string when no valid arrangement exists.
This problem appears in coding interviews and algorithm practice because it combines permutation generation, constraint checking, and simple string formatting into a single clear exercise. Understanding how to traverse possibilities efficiently and prune invalid states is the key to solving it reliably.
| Input Digits | Valid Permutations | Largest Time | Notes |
|---|---|---|---|
| [1,2,3,4] | 24 permutations | 23:41 | All digits used exactly once |
| [0,0,0,0] | 1 unique permutation | 00:00 | Earliest and latest coincide |
| [5,5,5,5] | 0 valid | "" | Hour 55 is invalid |
| [2,0,6,6] | 12 valid | 20:56 | Duplicates handled via set or sorting |
| [0,2,6,8] | 18 valid | 20:58 | Zero can start hour or minute |
Generate All Permutations Of Four Digits
To find the 949. largest time for given digits, start by generating all permutations of the four input digits. Since the array length is fixed, there are at most 4! equals 24 orderings, which is trivial to enumerate.
Use a standard permutation routine or language library to produce every ordering. From these, filter only candidates where the first two digits form a valid hour from 00 to 23 and the last two digits form a valid minute from 00 to 59.
Validate Hour And Minute Ranges
Each permutation must be checked against clock constraints to decide whether it represents a legal time. The hour part, built from the first two digits, must be in the range 00 to 23 inclusive.
The minute part, built from the last two digits, must be in the range 00 to 59 inclusive. Discard any permutation that violates either rule before comparing for maximality.
Compare Candidates To Find Maximum Time
With valid permutations identified, select the largest time by comparing total minutes, computed as hour times 60 plus minute. Track the best hour and minute pair as you scan through candidates.
Alternatively, compare lexicographically in HH:MM string form when leading zeros are preserved, but numeric minute comparison is straightforward and avoids string pitfalls for edge cases.
Format Output As HH:MM Or Return Empty
Once the optimal hour and minute are found, format them with leading zeros to ensure two-digit representation for both fields. If no valid permutation exists, return an empty string to signal impossibility.
This behavior is important for APIs and automated tests, because an empty result clearly indicates infeasibility rather than a default misleading time like 00:00.
Implement Robust Permutation Logic For Reliable Results
By following a systematic approach to permutation, validation, comparison, and formatting, you can handle all edge cases for the 949. largest time for given digits challenge. Use these practices to build concise, correct, and maintainable solutions.
- Enumerate all 24 permutations of the four input digits
- Filter permutations where hour is in 00–23 and minute is in 00–59
- Select the arrangement with the greatest total minutes
- Format hour and minute as two-digit strings in HH:MM
- Return an empty string when no valid arrangement exists
FAQ
Reader questions
What should I return if no valid time can be built from the digits?
Return an empty string, which signals that it is impossible to arrange the given digits into a legal HH:MM time.
Can the same digit be used more than once in a position?
No, you must use each of the four digits exactly once, reordering them to form the hour and minute components without repetition.
Why is 23:59 often the ideal largest time in examples?
23:59 represents the latest possible time on a 24-hour clock, so whenever the input digits allow constructing that combination it will be the correct answer.
How do leading zeros affect formatting of the result?
Both hour and minute must always be shown as two characters, so single-digit values like 6 must be rendered as 06 to preserve the HH:MM format.