FastPrepStable Unique Column Renames

Stable Unique Column Renames

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Problem statement

Process a sequence of table-schema snapshots. Each snapshot lists the currently visible raw column names in display order.

The first time a raw name appears, replace every . with _. The assigned display name must be unique case-insensitively across every name ever assigned. If the normalized base is already used, append _1, _2, and so on using the smallest available suffix.

A raw name keeps its assigned display name when it moves, disappears, or reappears in a later snapshot. Assigned names are never recycled. Return the renamed columns for every snapshot in the same shape and order.

Function

stableColumnNames(snapshots: String[][]) → String[][]

Examples

Example 1

snapshots = [["user.id","user_id"],["user_id","user.id"]]return = [["user_id","user_id_1"],["user_id_1","user_id"]]

The colliding raw names keep their first assigned names after reordering.

Example 2

snapshots = [["A"],["a"],["A"]]return = [["A"],["a_1"],["A"]]

Uniqueness is case-insensitive while exact raw-name identity is persistent.

Constraints

  • 0 <= snapshots.length <= 10000.
  • The total number of column occurrences is at most 200000.
  • Raw names are nonempty and unique within one snapshot.
  • Raw names contain letters, digits, underscores, and periods.

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public String[][] stableColumnNames(String[][] snapshots) {
    // Write your solution here.
}
snapshots[["user.id","user_id"],["user_id","user.id"]]
expected[["user_id", "user_id_1"], ["user_id_1", "user_id"]]
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