# 19-matching-MN-to-N

## 电信业务场景

套餐适用M:N→N条。多个合同关联多个套餐的组合匹配，输出按套餐件数(N件)的适用明细。

**M:N matching — output N records (one per detail match).**

Tests the scenario where both input files may contain duplicate keys.
The program performs a grouped match: for each key where at least one
master record exists, the program outputs every detail record for that
key, then skips all master records for that key.

## Test data

| File        | Records | Keys                          |
|-------------|---------|-------------------------------|
| master.dat  | 4       | KEY00001 (x2), KEY00002 (x2) |
| detail.dat  | 5       | KEY00001 (x2), KEY00003 (x3) |

- **Matched key:** KEY00001 -> 2 output records (2 detail records)
- **Unmatched master key:** KEY00002 (skipped)
- **Unmatched detail key:** KEY00003 (skipped)

## Algorithm

1. Read both files synchronously (both assumed sorted by key).
2. When keys match: output all detail records in the group, then skip all
   master records in the group.
3. When master key < detail key: skip all master records with that key
   (no matching detail).
4. When detail key < master key: skip all detail records with that key
   (no matching master).

## Expected output

- **output.dat:** 2 records x 45 bytes = 90 bytes
- Program displays: `19-matching-MN-to-N: PASS`
- Script displays: `19-matching-MN-to-N: ALL TESTS PASSED`