127 lines
3.0 KiB
Markdown
127 lines
3.0 KiB
Markdown
---
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id: 5900f3971000cf542c50feaa
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title: 'Problem 43: Sub-string divisibility'
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challengeType: 5
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forumTopicId: 302100
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dashedName: problem-43-sub-string-divisibility
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---
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# --description--
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The number, 1406357289, is a 0 to 9 pandigital number because it is made up of each of the digits 0 to 9 in some order, but it also has a rather interesting sub-string divisibility property.
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Let $d_1$ be the $1^{st}$ digit, $d_2$ be the $2^{nd}$ digit, and so on. In this way, we note the following:
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- ${d_2}{d_3}{d_4} = 406$ is divisible by 2
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- ${d_3}{d_4}{d_5} = 063$ is divisible by 3
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- ${d_4}{d_5}{d_6} = 635$ is divisible by 5
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- ${d_5}{d_6}{d_7} = 357$ is divisible by 7
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- ${d_6}{d_7}{d_8} = 572$ is divisible by 11
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- ${d_7}{d_8}{d_9} = 728$ is divisible by 13
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- ${d_8}{d_9}{d_{10}} = 289$ is divisible by 17
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Find the sum of all 0 to `n` pandigital numbers with sub-strings fulfilling `n - 2` of these divisibility properties.
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**Note:** Pandigital numbers starting with `0` are to be considered in the result.
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# --hints--
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`substringDivisibility(5)` should return a number.
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```js
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assert(typeof substringDivisibility(5) === 'number');
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```
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`substringDivisibility(5)` should return `12444480`.
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```js
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assert.strictEqual(substringDivisibility(5), 12444480)
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```
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`substringDivisibility(7)` should return `1099210170`.
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```js
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assert.strictEqual(substringDivisibility(7), 1099210170)
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```
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`substringDivisibility(8)` should return `1113342912`.
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```js
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assert.strictEqual(substringDivisibility(8), 1113342912)
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```
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`substringDivisibility(9)` should return `16695334890`.
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```js
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assert.strictEqual(substringDivisibility(9), 16695334890)
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```
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# --seed--
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## --seed-contents--
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```js
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function substringDivisibility(n) {
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return true;
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}
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substringDivisibility(5);
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```
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# --solutions--
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```js
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function substringDivisibility(n) {
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function isSubDivisable(digits) {
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const factors = [2, 3, 5, 7, 11, 13, 17];
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for (let i = 1; i < digits.length - 2; i++) {
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const subNumber = digits[i] * 100 + digits[i + 1] * 10 + digits[i + 2];
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if (subNumber % factors[i - 1] !== 0) {
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return false;
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}
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}
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return true;
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}
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function heapsPermutations(k, digits, conditionCheck, results) {
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if (k === 1) {
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if (conditionCheck(digits)) {
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const number = parseInt(digits.join(''), 10);
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results.push(number);
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}
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return;
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}
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heapsPermutations(k - 1, digits, conditionCheck, results);
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for (let i = 0; i < k - 1; i++) {
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if (k % 2 === 0) {
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[digits[i], digits[k - 1]] = [digits[k - 1], digits[i]];
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} else {
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[digits[0], digits[k - 1]] = [digits[k - 1], digits[0]];
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}
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heapsPermutations(k - 1, digits, conditionCheck, results);
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}
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return;
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}
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const allowedDigits = [...new Array(n + 1).keys()];
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const divisablePandigitals = [];
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heapsPermutations(
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allowedDigits.length,
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allowedDigits,
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isSubDivisable,
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divisablePandigitals
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);
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let sum = 0;
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for (let i = 0; i < divisablePandigitals.length; i++) {
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sum += divisablePandigitals[i];
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}
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return sum;
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}
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```
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