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Improved prime check and Fisher Yates #82

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Merged
merged 3 commits into from
Aug 15, 2015
Merged

Improved prime check and Fisher Yates #82

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51228e0
Improved prime factor check
infusion Aug 14, 2015
88b5454
Fixed fisheryates algorithm
infusion Aug 14, 2015
5066376
Mess with linter
infusion Aug 14, 2015
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50 changes: 19 additions & 31 deletions src/primes/is-prime.js
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Original file line number Diff line number Diff line change
Expand Up @@ -16,45 +16,33 @@
* console.log(isPrime(18)); // false
*/
exports.isPrime = function (number) {
if (number === 1) {

if (number < 2) {
return false;
}

} else if (number < 4) {
/**
* 2 and 3 are prime
*/
return true;
if (number % 2 === 0) {
return (number === 2);
}

} else if (number % 2 === 0) {
return false;
if (number % 3 === 0) {
return (number === 3);
}

} else if (number < 9) {
/**
* We have already excluded 4,6 and 8
*/
return true;
var horizon = Math.floor(Math.sqrt(number));
var factor = 5;

} else if (number % 3 === 0) {
return false;
while (factor <= horizon) {

} else {
/**
* 'number' rounded to the greatest integer 'rounded' so that:
* rounded * rounded <= number
*/
var rounded = Math.floor(Math.sqrt(number));
var factor = 5;
while (factor <= rounded) {
if (number % factor === 0) {
return false;
}
if (number % (factor + 2) === 0) {
return false;
}
factor += 6;
if (number % factor === 0) {
return false;
}
}

if (number % (factor + 2) === 0) {
return false;
}
factor += 6;
}
return true;
};

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4 changes: 2 additions & 2 deletions src/shuffle/fisheryates.js
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Original file line number Diff line number Diff line change
Expand Up @@ -21,8 +21,8 @@
var size = array.length;
var rand;
var temp;
for (var i = 1; i < size; i += 1) {
rand = Math.round(Math.random() * i);
for (var i = 0; i < size; i += 1) {
rand = Math.floor(i + Math.random() * (size - i));
temp = array[rand];
array[rand] = array[i];
array[i] = temp;
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