379. Most Common Lab Tool Pair

Most Common Lab Tool Pair

A school records the laboratory tools used during science experiments. The experiment records are grouped by class.

Each experiment is represented by a comma-separated string of tool names. Find the pair of different tools used together in the greatest number of experiments.

Implement the following method:

List<String> mostCommonToolPair( List<List<String>> experimentLogs )

experimentLogs.get(i) contains the experiments conducted by the ith class.
Each experiment is a comma-separated string such as "beaker,dropper,flask".
The method returns the two tool names in lexicographical order.

Rules

A pair must contain two different tools.
The pairs ("beaker", "flask") and ("flask", "beaker") are considered the same.
A repeated tool within the same experiment is considered only once.
One experiment may contribute several different tool pairs.
A pair's frequency is the number of experiments containing both tools.
If several pairs have the highest frequency, return the lexicographically smallest pair.
Compare pairs by their first tool name and then by their second tool name.

Constraints

1 ≤ experimentLogs.size() ≤ 1,000
1 ≤ experimentLogs.get(i).size() ≤ 1,000
The total number of experiments does not exceed 100,000.
Each experiment contains between 1 and 50 tool entries.
1 ≤ toolName.length() ≤ 30
Tool names contain lowercase English letters only.
At least one experiment contains two different tools.

Examples

Example 1

 mostCommonToolPair( experimentLogs = List.of( List.of( "microscope,slide,stain", "beaker,stirrer" ), List.of("slide,stain"), List.of("stain,slide,pipette"), List.of("microscope,slide") ) )

Output: List.of("slide", "stain")

The tools "slide" and "stain" occur together in three experiments, more than any other pair.

Example 2

 mostCommonToolPair( experimentLogs = List.of( List.of("clamp,clamp,stand,burner"), List.of("stand,burner"), List.of("clamp,stand") ) )

Output: List.of("burner", "stand")

Both ("burner", "stand") and ("clamp", "stand") occur twice. The first pair is lexicographically smaller. The repeated "clamp" in the first experiment does not increase any pair's frequency.

Example 3

 mostCommonToolPair( experimentLogs = List.of( List.of("funnel,spatula"), List.of("goggles,tripod"), List.of("tripod,goggles"), List.of("spatula,funnel") ) )

Output: List.of("funnel", "spatula")

The pairs ("funnel", "spatula") and ("goggles", "tripod") each occur twice. The pair beginning with "funnel" is lexicographically smaller.