Programming tips for solving problems

How to find even and odd numbers?

Following are a few techniques for finding even and odd numbers:

By using modulus

    const isEven = (n) => n % 2 == 0
    const isOdd = (n) => Math.abs(n % 2) == 1
    

By using a bit test

    const isEven = (n) => ~n & 1
    const isOdd = (n) => n & 1
    

How to count the total bits of a decimal number?

Following is a function to count the bit of a decimal number using the right shift operator:

    // 4 = 100, The total bit count is 1
    // 7 = 111, The total bit count is 3
    const countBit = (num) => {
        let sum = 0;
        while(num) {
            sum += num & 1;
            num = num >> 1;
        }
        return sum;
    };
    

Useful rules of XOR?

    The XOR with 0 and any number is equal to the number itself. 
    5 ^ 0 = 5
    

    The XOR of any number with itself is equal to 0. 
    5 ^ 5 = 0
    

    XOR is commutative, which means the order exchange will result in the same value.
    5 ^ 4 = 4 ^ 5
    

Get the frequency of an array of numbers using Map

    const getFreqMap = (item) => {
        const map = new Map();
        for(let i = 0; i < item.length; i++) {
            map.set(item[i], map.has(item[i]) ? map.get(item[i]) + 1 : 1);
        }
        return map;
    }
    

Get intersection of two arrays

    // Approach #1: 
    function intersection(nums1, nums2) {
        const set = new Set(nums1);
        return [...new Set(nums2.filter(n => set.has(n)))];
    }

    // Approach #2: 
    const intersect = arr2.map((x) => arr1.filter((y) => y == x)).flat();
    

Delete or remove array element by value

    const removeElm = (arr, item) => {
        const index = arr.indexOf(item);
        if (index !== -1) {
          arr.splice(index, 1);
        }        
    }
    

Check a char is a letter

    const isLetter = (l) => {
        return l.toLowerCase() !== l.toUpperCase();
    }
    

Bit count of an integer number

    const bitCount = (n) => {
      return n.toString(2).match(/1/g).length;
    }  
    

Check if a number is prime or not

    const isPrime = num => {
        for(let i = 2, s = Math.sqrt(num); i <= s; i++)
            if(num % i === 0) return false; 
        return num > 1;
    }
    

Check if the char is a vowel or not

    const isVowel = (c) => {
       return ['a', 'e', 'i', 'o', 'u'].indexOf(c.toLowerCase()) !== -1
    };
    

Find second highest number in an array of numbers

var secondHighest = function(s) {
    let firstLarge = -1, secondLarge = -1;
    for (let i = 0; i < s.length; i++) {
       const num = s[i];
       if (num > firstLarge) {
           secondLarge = firstLarge;
           firstLarge = num;
       } else if (num !== firstLarge && num > secondLarge) {
           secondLarge = num;
       }
    }    
    return secondLarge;
};
console.log(secondHighest([5, 13, 27, 9, 63, 63])) // 27

Is upper case or lower case letter in JavaScript

    const isUpperCase = (c) => c === c.toUpperCase();
    const isLowerCase = (c) => c === c.toLowerCase();

Check if a char is numeric or not

const isNumeric => (n) {
    return !isNaN(parseFloat(n)) && isFinite(n);
}

Get the digit count of a number

let num = 123;
let sum = 0;
while(num > 0) {
    sum += num % 10;
    num = Math.floor(num / 10);
}

In-Place number swapping using XOR

let x = 10, y = 5;
 
// 'x' binary (1010) and 'y' binary (0101)
x = x ^ y; // x now becomes 15 (1111)
y = x ^ y; // y becomes 10 (1010)
x = x ^ y; // x becomes 5 (0101)