From cc5000a9ef69d08fadf9aed6d6b96d0391d61317 Mon Sep 17 00:00:00 2001
From: wieerwill <robert.jeutter@gmx.de>
Date: Sun, 10 Dec 2023 13:34:53 +0100
Subject: [PATCH] solve Day09 in typescript

---
 Day09/ts/solution.ts | 78 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 Day09/ts/solution.ts

diff --git a/Day09/ts/solution.ts b/Day09/ts/solution.ts
new file mode 100644
index 0000000..1ddb532
--- /dev/null
+++ b/Day09/ts/solution.ts
@@ -0,0 +1,78 @@
+import fs from 'fs';
+
+function generateDifferenceTable(history: number[]): number[][] {
+    // Generates a difference table for a given history
+    let table: number[][] = [history];
+    while (!table[table.length - 1].every(value => value === 0)) {
+        let nextRow: number[] = [];
+        for (let i = 0; i < table[table.length - 1].length - 1; i++) {
+            nextRow.push(table[table.length - 1][i + 1] - table[table.length - 1][i]);
+        }
+        table.push(nextRow);
+    }
+    return table;
+}
+
+function extrapolatePreviousValue(table: number[][]): number {
+    // Extrapolates the previous value from the difference table
+    try {
+        for (let i = table.length - 2; i >= 0; i--) {
+            table[i].unshift(table[i][0] - table[i + 1][0]);
+        }
+        return table[0][0];
+    } catch (error) {
+        console.error(`Error in extrapolatePreviousValue: ${error}`);
+        throw error;
+    }
+}
+
+function solvePuzzle(filename: string): number {
+    // Solves the puzzle by reading histories from the file and summing their extrapolated previous values
+    try {
+        const data = fs.readFileSync(filename, 'utf8');
+        const lines = data.split('\n');
+        let total = 0;
+
+        for (const line of lines) {
+            if (line.trim() === '') continue;
+            const history = line.split(' ').map(Number);
+            const diffTable = generateDifferenceTable(history);
+            const prevValue = extrapolatePreviousValue(diffTable);
+            total += prevValue;
+        }
+
+        return total;
+    } catch (error) {
+        console.error(`Error processing file ${filename}: ${error}`);
+        throw error;
+    }
+}
+
+function test(): void {
+    // Runs the test using the test.txt file and asserts the expected outcome
+    const expected = 2; // Expected result from the test data for the second part
+    try {
+        const result = solvePuzzle('../test.txt');
+        console.assert(result === expected, `Test failed: Expected ${expected}, got ${result}`);
+        console.log('Test passed successfully.');
+    } catch (error) {
+        console.error(`Test failed: ${error}`);
+        process.exit(1);
+    }
+}
+
+function main(): void {
+    // Main function to run the test and then solve the puzzle
+    console.log('Running test for the second part...');
+    test();
+    console.log('Test completed. Solving the puzzle for the second part...');
+    try {
+        const result = solvePuzzle('../input.txt');
+        console.log(`Puzzle result for the second part: ${result}`);
+    } catch (error) {
+        console.error(`Error solving puzzle: ${error}`);
+        process.exit(1);
+    }
+}
+
+main();