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README.md

@@ -1,5 +1,7 @@
 # Japanese Era Calendar Scheme
 
+## 日本語暦変換プログラム
+
 If you've ever had to fill out paperwork in Japan, you know that the country uses two systems for counting dates: the western [Gregorian calendar](http://en.wikipedia.org/wiki/Gregorian_calendar), and the [Japanese era calendar scheme](http://en.wikipedia.org/wiki/Japanese_era_name), which uses the combination of the reigning Emperor's name and year since his birth.
 
 Write a program that takes a Gregorian date as an input, give the Japanese era date as an output. For example, with 2012-10-20 as an input, the output would be 平成24年10月20日.

yohei-cjs/Test

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+for date in    \
+    1920-05-07 \
+    1912-07-29 \
+    1912-07-30 \
+    2010-12-31 \
+; do
+    ./translate $date
+done | diff -u expected1 -

yohei-cjs/expected1

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+大正九年五月七日
+明治四十五年七月二十九日
+大正元年七月三十日
+平成二十二年十二月三十一日

yohei-cjs/translate

@@ -0,0 +1,32 @@
+#!/usr/bin/env ruby
+# -*- coding: utf-8 -*-
+
+# Convert number represented as a one- or two-digit string to kanji.
+def to_kanji(dd)
+    d1, d2 = dd.length == 1 ? ['0', dd[0]-48] : [dd[0]-48, dd[1]-48]
+    case d1 when 0 then ''
+            when 1 then 'JUU'
+                   else to_kanji_single(d1.to_i)        ;end \
+        + to_kanji_single(d2.to_s)
+end
+
+def to_kanji_single(n)
+    n.to_s
+end
+
+date  = ARGV[0]
+match = date.match(/^(\d{4})-(\d\d)-(\d\d)$/)
+raise "Unparsable date: #{ARGV[0]}" unless match
+year, month, day = match[1].to_i, match[2], match[3]
+
+eras = [
+    ['1989-01-08', '平成'],
+    ['1926-12-25', '昭和'],
+    ['1912-07-30', '大正'],
+    ['1868-09-08', '明治'],
+]
+era_start, era = eras.drop_while { |start, era| start > date }[0]
+era_start_year = Integer(era_start.match(/^\d{4}/)[0])
+
+printf("%s%s年%s月%s日\n", era, to_kanji((year-era_start_year+1).to_s),
+    to_kanji(month), to_kanji(day))