Algorithm Hacks

• Truth Table
• Binary to Hex/Decimal
• Fibonacci
• Palindrome
• Other (extra)

Truth Table

const table = [
    [0, 0],
    [0, 1],
    [1, 0],
    [1, 1]
];

const singleColumnTable = [0, 1];

const binaryOps = {
    "AND": (a, b) => a & b,
    "OR": (a, b) => a | b,
    "XOR": (a, b) => a ^ b,
}

const unaryOps = {
    "NOT": (a) => +!a
}

let s = ""
for (const [op, fn] of Object.entries(binaryOps)) {
    s += `<h1>${op}</h1>\n`
    for (const [a, b] of table) {
        s += `<p>${a} ${op} ${b} = ${fn(a, b)}</p>\n`
    }
}

for (const [op, fn] of Object.entries(unaryOps)) {
    s += `<h1>${op}</h1>\n`
    for (const a of singleColumnTable) {
        s += `<p>${op} ${a} = ${fn(a)}</p>\n`
    }
}

document.getElementById("table").innerHTML = s;

Binary to Hex/Decimal

const binaryString = "11101011101";
const hexValue = (bin) => parseInt(bin, 2).toString(16);
const decValue = (bin) => parseInt(bin, 2).toString(10);

console.log(hexValue(binaryString));
console.log(decValue(binaryString));

75d
1885

binaryString = "11101011101"

def hexValue(bin):
    return hex(int(bin, 2))

def decValue(bin):
    return str(int(bin, 2))

print(hexValue(binaryString))
print(decValue(binaryString))

0x75d
1885

Fibonacci

const fib = (n) => {
    if (n === 0 || n === 1) return n
    return fib(n - 1) + fib(n - 2)
}

for (let i = 0; i< 10; i++) {
    console.log(fib(i))
}

0
1
1
2
3
5
8
13
21
34

def fib(n):
    if n == 0 or n == 1:
        return n
    return fib(n - 1) + fib(n - 2)

for i in range(10):
    print(fib(i))

0
1
1
2
3
5
8
13
21
34

Palindrome

const revString = (str) => str.split("").reverse().join("")
const isPalindrome = (str) => str === revString(str.split("").reverse().join(""));
const createPalindrome = (str) => str + revString(str)

console.log(revString("abcd"))
console.log(isPalindrome("abba"))
console.log(createPalindrome("abcdef"))

dcba
true
abcdeffedcba

def rev_string(str):
    return str[::-1]

def is_palindrome(str):
    return rev_string(str) == str

def create_palindrome(str):
    return str + rev_string(str)

print(rev_string("abcd"))
print(is_palindrome("abba"))
print(create_palindrome("abcdef"))

dcba
True
abcdeffedcba

Other (extra)

const binarySearch1 = (xs, x, start, end) => {
    if (start > end) return -1;
    
    const mid = Math.floor((start+end) / 2);
    if (xs[mid] === x) return mid;
    if (xs[mid] > x) return binarySearch1(xs, x, start,  mid-1);
    if (xs[mid] < x) return binarySearch1(xs, x, mid+1,  end);
}

const binarySearch = (xs, x) => binarySearch1(xs, x, 0, xs.length - 1)

const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
const needle = 4
console.log(`found ${needle} at idx ${binarySearch(arr, needle)}`)

found 4 at idx 3

import math

def binary_search1(xs, x, start, end):
    if start > end: return -1
    mid = math.floor((start + end) / 2)
    if xs[mid] == x: return mid
    if xs[mid] > x: return binary_search1(xs, x, start,  mid-1)
    if xs[mid] < x: return binary_search1(xs, x, mid+1,  end)

def binary_search(xs, x):
    return binary_search1(xs, x, 0, len(xs) - 1)

arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
needle = 4
print("found {} at idx {}".format(needle, binary_search(arr, needle)))

found 4 at idx 3