Factorial with base 1000.

2022/03/algorithms/factorial2.js

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+'use strict';
+
+process.stdin.resume();
+process.stdin.setEncoding('utf-8');
+
+let inputString = '';
+let currentLine = 0;
+
+process.stdin.on('data', function(inputStdin) {
+    inputString += inputStdin;
+});
+
+process.stdin.on('end', function() {
+    inputString = inputString.split('\n');
+
+    main();
+});
+
+process.on('SIGINT', function() {
+    inputString = inputString.split('\n');
+
+    main();
+    process.exit(0);
+});
+
+function readLine() {
+    return inputString[currentLine++];
+}
+
+/*
+ * Complete the 'extraLongFactorials' function below.
+ *
+ * The function accepts INTEGER n as parameter.
+ */
+
+// the idea to store digits in array
+// but the system is 1000 base instead of 10
+// just for printing issues
+
+function convert_to(n) {
+    let res = [];
+    let digit;
+    do {
+        digit = n % 1000;
+        res.unshift(digit);
+        n = Math.floor(n / 1000);
+    } while (n > 0);
+    
+    return res;
+}
+
+function sum(a, b) {
+    let da, db, shift = 0, res;
+    let digits = [];
+    while (a.length || b.length) {
+        da = a.length ? a.pop() : 0;
+        db = b.length ? b.pop() : 0;
+        res = da + db + shift;
+        digits.unshift(res % 1000);
+        shift = Math.floor(res / 1000);
+    }
+    if (shift > 0) {
+        digits.unshift(shift);
+    }
+    return digits;
+}
+
+function multiply(a, b) {
+    // console.log('multiply', a, b);
+    let n = a.length;
+    let m = b.length;
+    let da, db, shift = 0, res;
+    
+    let offsetArray = [];
+    let subSum;
+    let sumAll = [0];
+    
+    for (let i = m - 1; i >= 0; i--) {
+        subSum = [...offsetArray];
+        offsetArray.push(0);
+        for (let j = n - 1; j >= 0; j--) {
+            res = b[i] * a[j] + shift;
+            subSum.unshift(res % 1000);
+            shift = Math.floor(res / 1000);
+        }
+        if (shift > 0) {
+            subSum.unshift(shift);
+        }
+        // console.log('Subsum', subSum);
+        sumAll = sum(sumAll, subSum);
+        // console.log('Summed', sumAll);
+    }
+    return sumAll;
+}
+
+function extraLongFactorials(n) {
+    let m = [1];
+    let factor = [0];
+    for (let i = 0; i < n; i++) {
+        factor = sum(factor, [1]);
+        console.log(`Factor`, m, factor);
+        m = multiply(m, factor);
+    }
+
+    console.log(`Result`, m);
+
+    let s = "" + m[0];
+    for (let i = 1; i < m.length; i++) {
+        s += ("" + m[i]).padStart(3, "0");
+    }
+
+    console.log(s);
+}
+
+function main() {
+    const n = parseInt(readLine().trim(), 10);
+
+    extraLongFactorials(n);
+}