# 求和

# 1. sum

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const sum = (...arr) => [...arr].reduce((acc, val) => acc + val, 0);

EXAMPLES:

sum(1, 2, 3, 4); // 10
sum(...[1, 2, 3, 4]); // 10

# 2. sumPower

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const sumPower = (end, power = 2, start = 1) =>
  Array(end + 1 - start)
    .fill(0)
    .map((x, i) => (i + start) ** power)
    .reduce((a, b) => a + b, 0);

EXAMPLES:

sumPower(10); // 385
sumPower(10, 3); // 3025
sumPower(10, 3, 5); // 2925

# 3. accumulate

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const accumulate = (...nums) => nums.reduce((acc, n) => [...acc, n + +acc.slice(-1)],[]);

EXAMPLES:

accumulate(1, 2, 3, 4); // [1, 3, 6, 10]
accumulate(...[1, 2, 3, 4]); // [1, 3, 6, 10]

# 4. distance(平方和后平方根)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);

EXAMPLES:

distance(1, 1, 2, 3); // 2.23606797749979

# 5. factorial(递归)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const factorial = n =>
  n < 0
    ? (() => {
        throw new TypeError('Negative numbers are not allowed!');
      })()
    : n <= 1
    ? 1
    : n * factorial(n - 1);

EXAMPLES:

factorial(6); // 720

# 均值

# 1. average

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const average = (...nums) => nums.reduce((acc, val) => acc + val, 0) / nums.length;

EXAMPLES:

average(...[1, 2, 3]); // 2
average(1, 2, 3); // 2

# 2. averageBy(by)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const averageBy = (arr, fn) =>
  arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => acc + val, 0) /
  arr.length;

EXAMPLES:

averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 5
averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 5

# 相等

# 1. approximatelyEqual(约)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const approximatelyEqual = (v1, v2, epsilon = 0.001) => Math.abs(v1 - v2) < epsilon;

EXAMPLES:

approximatelyEqual(Math.PI / 2.0, 1.5708); // true

# 2. isNegativeZero(-0)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const isNegativeZero = val => val === 0 && 1 / val === -Infinity;

EXAMPLES:

isNegativeZero(-0); // true
isNegativeZero(0); // false

# 3. isPowerOfTwo(2的幂)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const isPowerOfTwo = n => !!n && (n & (n - 1)) == 0;

EXAMPLES:

isPowerOfTwo(0); // false
isPowerOfTwo(1); // true
isPowerOfTwo(8); // true

# 随机

# 1. randomHexColorCode(颜色)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const randomHexColorCode = () => {
  let n = (Math.random() * 0xfffff * 1000000).toString(16);
  return '#' + n.slice(0, 6);
};

EXAMPLES:

randomHexColorCode(); // "#e34155"

# 2. randomIntArrayInRange(区间)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const randomIntArrayInRange = (min, max, n = 1) =>
  Array.from({ length: n }, () => Math.floor(Math.random() * (max - min + 1)) + min);

EXAMPLES:

randomIntArrayInRange(12, 35, 10); // [ 34, 14, 27, 17, 30, 27, 20, 26, 21, 14 ]

# 区间

# 1. clampNumber(更近)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const clampNumber = (num, [a, b]) => Math.max(Math.min(num, Math.max(a, b)), Math.min(a, b));

EXAMPLES:

clampNumber(2, [3, 5]); // 3
clampNumber(1, [-1, -5]); // -1

# 2. geometricProgression(生成)

FROM

30 seconds of code (Math)

DETAIL:

初看时有点懵。

FUNCTION:

const geometricProgression = (end, start = 1, step = 2) =>
  Array.from({ length: Math.floor(Math.log(end / start) / Math.log(step)) + 1 }).map(
    (v, i) => start * step ** i
  );

EXAMPLES:

geometricProgression(256); // [1, 2, 4, 8, 16, 32, 64, 128, 256]
geometricProgression(256, 3); // [3, 6, 12, 24, 48, 96, 192]
geometricProgression(256, 1, 4); // [1, 4, 16, 64, 256]

# 3. inRange(判断)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const inRange = (n, start, end = null) => {
  if (end && start > end) [end, start] = [start, end];
  return end == null ? n >= 0 && n < start : n >= start && n < end;
};

EXAMPLES:

inRange(3, 2, 5); // true
inRange(3, 4); // true
inRange(2, 3, 5); // false
inRange(3, 2); // false

# 4. mapNumRange(区间映射)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const mapNumRange = (num, inMin, inMax, outMin, outMax) =>
  ((num - inMin) * (outMax - outMin)) / (inMax - inMin) + outMin;

EXAMPLES:

mapNumRange(5, 0, 10, 0, 100); // 50

# 5. toSafeInteger(安全整数)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const toSafeInteger = num =>
  Math.round(Math.max(Math.min(num, Number.MAX_SAFE_INTEGER), Number.MIN_SAFE_INTEGER));

EXAMPLES:

toSafeInteger('3.2'); // 3
toSafeInteger(Infinity); // 9007199254740991

# 向量

# 1. vectorAngle(角度)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const vectorAngle = (x, y) => {
  let mX = Math.sqrt(x.reduce((acc, n) => acc + Math.pow(n, 2), 0));
  let mY = Math.sqrt(y.reduce((acc, n) => acc + Math.pow(n, 2), 0));
  return Math.acos(x.reduce((acc, n, i) => acc + n * y[i], 0) / (mX * mY));
};

EXAMPLES:

vectorAngle([3, 4], [4, 3]); // 0.283794109208328

# 2. vectorDistance(距离)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const vectorDistance = (x, y) =>
  Math.sqrt(x.reduce((acc, val, i) => acc + Math.pow(val - y[i], 2), 0));

EXAMPLES:

vectorDistance([10, 0, 5], [20, 0, 10]); // 11.180339887498949

# 转换

# 1. celsiusToFahrenheit(°C => °F)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const celsiusToFahrenheit = degrees => 1.8 * degrees + 32;

EXAMPLES:

celsiusToFahrenheit(33); // 91.4

# 2. fahrenheitToCelsius(°F => °C)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const fahrenheitToCelsius = degrees => ((degrees - 32) * 5) / 9;

EXAMPLES:

fahrenheitToCelsius(32); // 0

# 3. degreesToRads(角度 => 弧度)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const degreesToRads = deg => (deg * Math.PI) / 180.0;

EXAMPLES:

degreesToRads(90.0); // ~1.5708

# 4. radsToDegrees(弧度 => 角度)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const radsToDegrees = rad => (rad * 180.0) / Math.PI;

EXAMPLES:

radsToDegrees(Math.PI / 2); // 90

# 5. toCurrency(货币)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const toCurrency = (n, curr, LanguageFormat = undefined) =>
  Intl.NumberFormat(LanguageFormat, { style: 'currency', currency: curr }).format(n);

EXAMPLES:

toCurrency(123456.789, 'EUR'); // €123,456.79  | currency: Euro | currencyLangFormat: Local
toCurrency(123456.789, 'USD', 'en-us'); // $123,456.79  | currency: US Dollar | currencyLangFormat: English (United States)
toCurrency(123456.789, 'USD', 'fa'); // ۱۲۳٬۴۵۶٫۷۹ ؜$ | currency: US Dollar | currencyLangFormat: Farsi
toCurrency(322342436423.2435, 'JPY'); // ¥322,342,436,423 | currency: Japanese Yen | currencyLangFormat: Local
toCurrency(322342436423.2435, 'JPY', 'fi'); // 322 342 436 423 ¥ | currency: Japanese Yen | currencyLangFormat: Finnish

# 6. toOrdinalSuffix(序数)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const toOrdinalSuffix = num => {
  const int = parseInt(num),
    digits = [int % 10, int % 100],
    ordinals = ['st', 'nd', 'rd', 'th'],
    oPattern = [1, 2, 3, 4],
    tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
  return oPattern.includes(digits[0]) && !tPattern.includes(digits[1])
    ? int + ordinals[digits[0] - 1]
    : int + ordinals[3];
};

EXAMPLES:

toOrdinalSuffix('123'); // "123rd"

# 7. digitize(string => number)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const digitize = n => [...`${n}`].map(i => parseInt(i));

EXAMPLES:

digitize(123); // [1, 2, 3]

# 8. sdbm

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const sdbm = str => {
  let arr = str.split('');
  return arr.reduce(
    (hashCode, currentVal) =>
      (hashCode = currentVal.charCodeAt(0) + (hashCode << 6) + (hashCode << 16) - hashCode),
    0
  );
};

EXAMPLES:

sdbm('name'); // -3521204949

# Math

# 1. binomialCoefficient(二项式系数)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const binomialCoefficient = (n, k) => {
  if (Number.isNaN(n) || Number.isNaN(k)) return NaN;
  if (k < 0 || k > n) return 0;
  if (k === 0 || k === n) return 1;
  if (k === 1 || k === n - 1) return n;
  if (n - k < k) k = n - k;
  let res = n;
  for (let j = 2; j <= k; j++) res *= (n - j + 1) / j;
  return Math.round(res);
};

EXAMPLES:

binomialCoefficient(8, 2); // 28

# 2. elo

FROM

30 seconds of code (Math)

DETAIL:

等级分 的实现。

FUNCTION:

const elo = ([...ratings], kFactor = 32, selfRating) => {
  const [a, b] = ratings;
  const expectedScore = (self, opponent) => 1 / (1 + 10 ** ((opponent - self) / 400));
  const newRating = (rating, i) =>
    (selfRating || rating) + kFactor * (i - expectedScore(i ? a : b, i ? b : a));
  if (ratings.length === 2) return [newRating(a, 1), newRating(b, 0)];

  for (let i = 0, len = ratings.length; i < len; i++) {
    let j = i;
    while (j < len - 1) {
      j++;
      [ratings[i], ratings[j]] = elo([ratings[i], ratings[j]], kFactor);
    }
  }
  return ratings;
};

EXAMPLES:

// Standard 1v1s
elo([1200, 1200]); // [1216, 1184]
elo([1200, 1200], 64); // [1232, 1168]
// 4 player FFA, all same rank
elo([1200, 1200, 1200, 1200]).map(Math.round); // [1246, 1215, 1185, 1154]
/*
For teams, each rating can adjusted based on own team's average rating vs.
average rating of opposing team, with the score being added to their
own individual rating by supplying it as the third argument.
*/

# 3. fibonacci(斐波那契数列)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const fibonacci = n =>
  Array.from({ length: n }).reduce(
    (acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i),
    []
  );

EXAMPLES:

fibonacci(6); // [0, 1, 1, 2, 3, 5]

# 4. gcd(最大公约数)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const gcd = (...arr) => {
  const _gcd = (x, y) => (!y ? x : gcd(y, x % y));
  return [...arr].reduce((a, b) => _gcd(a, b));
};

EXAMPLES:

gcd(8, 36); // 4
gcd(...[12, 8, 32]); // 4

# 5. lcm(最小公倍数)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const lcm = (...arr) => {
  const gcd = (x, y) => (!y ? x : gcd(y, x % y));
  const _lcm = (x, y) => (x * y) / gcd(x, y);
  return [...arr].reduce((a, b) => _lcm(a, b));
};

EXAMPLES:

lcm(12, 7); // 84
lcm(...[1, 3, 4, 5]); // 60

# 6. hammingDistance(汉明距离)

FROM

30 seconds of code (Math)

DETAIL:

^ 按位异或操作。

FUNCTION:

const hammingDistance = (num1, num2) => ((num1 ^ num2).toString(2).match(/1/g) || '').length;

EXAMPLES:

hammingDistance(2, 3); // 1

# 7. isPrime(质数)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const isPrime = num => {
  const boundary = Math.floor(Math.sqrt(num));
  for (var i = 2; i <= boundary; i++) if (num % i === 0) return false;
  return num >= 2;
};

EXAMPLES:

isPrime(11); // true

# 8. primes(质数)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const primes = num => {
  let arr = Array.from({ length: num - 1 }).map((x, i) => i + 2),
    sqroot = Math.floor(Math.sqrt(num)),
    numsTillSqroot = Array.from({ length: sqroot - 1 }).map((x, i) => i + 2);
  numsTillSqroot.forEach(x => (arr = arr.filter(y => y % x !== 0 || y === x)));
  return arr;
};

EXAMPLES:

primes(10); // [2,3,5,7]

# 9. median(中位数)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const median = arr => {
  const mid = Math.floor(arr.length / 2),
    nums = [...arr].sort((a, b) => a - b);
  return arr.length % 2 !== 0 ? nums[mid] : (nums[mid - 1] + nums[mid]) / 2;
};

EXAMPLES:

median([5, 6, 50, 1, -5]); // 5

# 10. standardDeviation(标准差)

FROM

30 seconds of code (Math)

DETAIL:

暂无。

FUNCTION:

const standardDeviation = (arr, usePopulation = false) => {
  const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
  return Math.sqrt(
    arr.reduce((acc, val) => acc.concat((val - mean) ** 2), []).reduce((acc, val) => acc + val, 0) /
      (arr.length - (usePopulation ? 0 : 1))
  );
};

EXAMPLES:

standardDeviation([10, 2, 38, 23, 38, 23, 21]); // 13.284434142114991 (sample)
standardDeviation([10, 2, 38, 23, 38, 23, 21], true); // 12.29899614287479 (population)