From a9e2661dcdd29880d822a36071f9905d5a8184f8 Mon Sep 17 00:00:00 2001
From: Eric Lavault <39483232+lvlte@users.noreply.github.com>
Date: Tue, 5 Oct 2021 18:06:50 +0200
Subject: [PATCH 1/4] Project Euler : add solution for problem 16 (Power digit
 sum).

---
 Project-Euler/Problem016.js | 45 +++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 Project-Euler/Problem016.js

diff --git a/Project-Euler/Problem016.js b/Project-Euler/Problem016.js
new file mode 100644
index 0000000000..6adf3d9e63
--- /dev/null
+++ b/Project-Euler/Problem016.js
@@ -0,0 +1,45 @@
+/**
+ * Problem 16 - Power digit sum
+ *
+ * @see {@link https://projecteuler.net/problem=16}
+ *
+ * 2¹⁵ = 32768 and the sum of its digits is 3 + 2 + 7 + 6 + 8 = 26.
+ *
+ * What is the sum of the digits of the number 2¹⁰⁰⁰ ?
+ */
+
+/**
+ * Returns the power digit sum of n^pow.
+ *
+ * @param {number} [n=2]
+ * @param {number} [pow=1000]
+ * @returns {number}
+ */
+const powerDigitSum = function (n = 2, pow = 1000) {
+  // The idea is to consider each digit (d*10^exp) separately, right-to-left.
+  // digits = [units, tens, ...]
+
+  const digits = [n]
+  let p = 1
+
+  while (++p <= pow) {
+    let carry = 0
+    for (let exp = 0; exp < digits.length; exp++) {
+      const prod = digits[exp] * n + carry
+      carry = Math.floor(prod / 10)
+      digits[exp] = prod % 10
+    }
+    while (carry > 0) {
+      digits.push(carry % 10)
+      carry = Math.floor(carry / 10)
+    }
+  }
+
+  // (digits are reversed but we only want the sum so it doesn't matter)
+
+  return digits.reduce((prev, current) => prev + current, 0)
+}
+
+console.log('Power digit sum of 2^1000 :', powerDigitSum())
+
+module.exports = powerDigitSum

From 22e194ed392fdc1f6677b258cbadc40403a59718 Mon Sep 17 00:00:00 2001
From: Eric Lavault <39483232+lvlte@users.noreply.github.com>
Date: Tue, 5 Oct 2021 18:11:21 +0200
Subject: [PATCH 2/4] Add tests for ProjectEuler problem 16 (Jest).

---
 Project-Euler/test/Problem016.test.js | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
 create mode 100644 Project-Euler/test/Problem016.test.js

diff --git a/Project-Euler/test/Problem016.test.js b/Project-Euler/test/Problem016.test.js
new file mode 100644
index 0000000000..0b707ef4c9
--- /dev/null
+++ b/Project-Euler/test/Problem016.test.js
@@ -0,0 +1,16 @@
+const powerDigitSum = require('../Problem016')
+
+describe('Check Problem 16 - Power digit sum', () => {
+  it('Power digit sum of 2^15', () => {
+    expect(powerDigitSum(2, 15)).toBe(26)
+  })
+
+  it('Power digit sum of 2^1000', () => {
+    expect(powerDigitSum()).toBe(1366)
+    expect(powerDigitSum(2, 1000)).toBe(1366)
+  })
+
+  it('Power digit sum of 3^5000', () => {
+    expect(powerDigitSum(3, 5000)).toBe(11097)
+  })
+})

From 8afef50cb7b6b06c83e93fc4ea8d38df5fe6325c Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Tue, 5 Oct 2021 16:12:48 +0000
Subject: [PATCH 3/4] Auto-update DIRECTORY.md

---
 DIRECTORY.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index d63e09657f..34e83af682 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -190,6 +190,7 @@
   * [Problem013](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem013.js)
   * [Problem014](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem014.js)
   * [Problem015](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem015.js)
+  * [Problem016](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem016.js)
   * [Problem020](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem020.js)
   * [Problem1](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem1.js)
   * [Problem10](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem10.js)

From 52de0391845c8c83a66b9d42e25cff1616e94e53 Mon Sep 17 00:00:00 2001
From: Eric Lavault <39483232+lvlte@users.noreply.github.com>
Date: Fri, 8 Oct 2021 13:21:01 +0200
Subject: [PATCH 4/4] Use ESM syntax and remove console.log()

---
 Project-Euler/Problem016.js           | 4 +---
 Project-Euler/test/Problem016.test.js | 2 +-
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/Project-Euler/Problem016.js b/Project-Euler/Problem016.js
index 6adf3d9e63..d3c92f3eeb 100644
--- a/Project-Euler/Problem016.js
+++ b/Project-Euler/Problem016.js
@@ -40,6 +40,4 @@ const powerDigitSum = function (n = 2, pow = 1000) {
   return digits.reduce((prev, current) => prev + current, 0)
 }
 
-console.log('Power digit sum of 2^1000 :', powerDigitSum())
-
-module.exports = powerDigitSum
+export { powerDigitSum }
diff --git a/Project-Euler/test/Problem016.test.js b/Project-Euler/test/Problem016.test.js
index 0b707ef4c9..9bb229f1a0 100644
--- a/Project-Euler/test/Problem016.test.js
+++ b/Project-Euler/test/Problem016.test.js
@@ -1,4 +1,4 @@
-const powerDigitSum = require('../Problem016')
+import { powerDigitSum } from '../Problem016'
 
 describe('Check Problem 16 - Power digit sum', () => {
   it('Power digit sum of 2^15', () => {