fix(curriculum): rework Project Euler 80 (#42128)

* fix: rework challenge to use argument in function

* fix: add solution

curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-80-square-root-digital-expansion.md

@@ -10,22 +10,34 @@ dashedName: problem-80-square-root-digital-expansion
 
 It is well known that if the square root of a natural number is not an integer, then it is irrational. The decimal expansion of such square roots is infinite without any repeating pattern at all.
 
-The square root of two is 1.41421356237309504880..., and the digital sum of the first one hundred decimal digits is 475.
+The square root of two is `1.41421356237309504880...`, and the digital sum of the first one hundred decimal digits is `475`.
 
-For the first one hundred natural numbers, find the total of the digital sums of the first one hundred decimal digits for all the irrational square roots.
+For the first `n` natural numbers, find the total of the digital sums of the first one hundred decimal digits for all the irrational square roots.
 
 # --hints--
 
-`sqrtDigitalExpansion()` should return a number.
+`sqrtDigitalExpansion(2)` should return a number.
 
 ```js
-assert(typeof sqrtDigitalExpansion() === 'number');
+assert(typeof sqrtDigitalExpansion(2) === 'number');
 ```
 
-`sqrtDigitalExpansion()` should return 40886.
+`sqrtDigitalExpansion(2)` should return `475`.
 
 ```js
-assert.strictEqual(sqrtDigitalExpansion(), 40886);
+assert.strictEqual(sqrtDigitalExpansion(2), 475);
+```
+
+`sqrtDigitalExpansion(50)` should return `19543`.
+
+```js
+assert.strictEqual(sqrtDigitalExpansion(50), 19543);
+```
+
+`sqrtDigitalExpansion(100)` should return `40886`.
+
+```js
+assert.strictEqual(sqrtDigitalExpansion(100), 40886);
 ```
 
 # --seed--
@@ -33,16 +45,65 @@ assert.strictEqual(sqrtDigitalExpansion(), 40886);
 ## --seed-contents--
 
 ```js
-function sqrtDigitalExpansion() {
+function sqrtDigitalExpansion(n) {
 
   return true;
 }
 
-sqrtDigitalExpansion();
+sqrtDigitalExpansion(2);
 ```
 
 # --solutions--
 
 ```js
-// solution required
+function sqrtDigitalExpansion(n) {
+  function sumDigits(number) {
+    let sum = 0;
+    while (number > 0n) {
+      let digit = number % 10n;
+      sum += parseInt(digit, 10);
+      number = number / 10n;
+    }
+    return sum;
+  }
+
+  function power(numberA, numberB) {
+    let result = 1n;
+    for (let b = 0; b < numberB; b++) {
+      result = result * BigInt(numberA);
+    }
+    return result;
+  }
+
+  // Based on http://www.afjarvis.staff.shef.ac.uk/maths/jarvisspec02.pdf
+  function expandSquareRoot(number, numDigits) {
+    let a = 5n * BigInt(number);
+    let b = 5n;
+    const boundaryWithNeededDigits = power(10, numDigits + 1);
+
+    while (b < boundaryWithNeededDigits) {
+      if (a >= b) {
+        a = a - b;
+        b = b + 10n;
+      } else {
+        a = a * 100n;
+        b = (b / 10n) * 100n + 5n;
+      }
+    }
+    return b / 100n;
+  }
+
+  let result = 0;
+  let nextPerfectRoot = 1;
+  const requiredDigits = 100;
+  for (let i = 1; i <= n; i++) {
+    if (nextPerfectRoot ** 2 === i) {
+      nextPerfectRoot++;
+      continue;
+    }
+    result += sumDigits(expandSquareRoot(i, requiredDigits));
+  }
+
+  return result;
+}
 ```