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Get union of arrays

Nov 19, 2022CodeCatch
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Flatten an array

Nov 19, 2022CodeCatch

0 likes • 3 views

const flat = arr => [].concat.apply([], arr.map(a => Array.isArray(a) ? flat(a) : a));
// Or
const flat = arr => arr.reduce((a, b) => Array.isArray(b) ? [...a, ...flat(b)] : [...a, b], []);
// Or
// See the browser compatibility at https://caniuse.com/#feat=array-flat
const flat = arr => arr.flat();
// Example
flat(['cat', ['lion', 'tiger']]); // ['cat', 'lion', 'tiger']

count substrings

Nov 19, 2022CodeCatch

0 likes • 0 views

const countSubstrings = (str, searchValue) => {
let count = 0,
i = 0;
while (true) {
const r = str.indexOf(searchValue, i);
if (r !== -1) [count, i] = [count + 1, r + 1];
else return count;
}
};
countSubstrings('tiktok tok tok tik tok tik', 'tik'); // 3
countSubstrings('tutut tut tut', 'tut'); // 4

Invert Binary Tree

Oct 15, 2022CodeCatch

2 likes • 8 views

var invertTree = function(root) {
const reverseNode = node => {
if (node == null) {
return null
}
reverseNode(node.left);
reverseNode(node.right);
let holdLeft = node.left;
node.left = node.right;
node.right = holdLeft;
return node;
}
return reverseNode(root);
};

Mongoose Model

Mar 11, 2021C S

0 likes • 1 view

const mongoose = require('mongoose')
const UserSchema = new mongoose.Schema({
username: {
type: String,
required: true
},
email: {
type: String,
unique: true,
required: true
},
password: {
type: String,
required: true
},
date: {
type: Date,
default: Date.now
}
})
module.exports = User = mongoose.model('user', UserSchema)

binomial coefficient

Nov 19, 2022CodeCatch

0 likes • 0 views

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);
};
binomialCoefficient(8, 2); // 28

arithmetic progression

Nov 19, 2022CodeCatch

0 likes • 2 views

const arithmeticProgression = (n, lim) =>
Array.from({ length: Math.ceil(lim / n) }, (_, i) => (i + 1) * n );
arithmeticProgression(5, 25); // [5, 10, 15, 20, 25]