From 40fb4d1b3581fd5ef1c2f87589d1e81ee4f47dd2 Mon Sep 17 00:00:00 2001
From: b1ancuito <460abe@gmail.com>
Date: Sun, 18 Jan 2026 10:18:23 +0900
Subject: [PATCH] =?UTF-8?q?=E3=83=A9=E3=83=B3=E3=82=AD=E3=83=B3=E3=82=B0?=
 =?UTF-8?q?=E3=81=AE=E5=AE=9F=E8=A3=85=E5=AE=8C=E4=BA=86?=
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---
 app.js | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/app.js b/app.js
index ad9a93a..70c8199 100644
--- a/app.js
+++ b/app.js
@@ -1 +1,46 @@
 'use strict';
+const fs = require('node:fs');
+const readline = require('node:readline');
+const rs = fs.createReadStream('./popu-pref.csv');
+const rl = readline.createInterface({ input:rs });
+const prefectureDataMap = new Map();
+
+rl.on('line', lineString => {
+  const columns = lineString.split(',');
+  const year = parseInt(columns[0]);
+  const prefecture = columns[1];
+  const popu = parseInt(columns[3]);
+  if (year === 2016 || year === 2021){
+    let value = null;
+    if (prefectureDataMap.has(prefecture)){
+      value = prefectureDataMap.get(prefecture);
+      console.log('データあったよ！')
+    }else {
+      value = {
+        before: 0,
+        after: 0,
+        change: null
+      }
+      console.log('データなかったよ！')
+    }
+    if (year === 2016) {
+      value.before = popu;
+    }
+    if (year === 2021) {
+      value.after = popu;
+    }
+    prefectureDataMap.set(prefecture, value);
+  }
+});
+rl.on('close', () => {
+  for (const [key, value] of prefectureDataMap) {
+    value.change = value.after / value.before;
+  }
+  const rankingArray = Array.from(prefectureDataMap).sort((pair1, pair2) => {
+    return pair2[1].change - pair1[1].change;
+  });
+ const rankingStrings = rankingArray.map(([key, value]) => {
+  return `${key}: ${value.before} => ${value.after} 変化率：${value.change}`;
+ });
+ console.log(rankingStrings);
+});
\ No newline at end of file