Javascript:Leet Code -Find pair of number in array whose sum equal to target

Find a pair of number from array whose sum is equal to target

nums = [2, 7, 11, 15]

target = 9

function targetSumPair(nums, target) {

    arr = []

    for (let i = 0; i < nums.length; i++) {

        for (let j = i + 1; j < nums.length; j++) {

            if(nums[i]>target && nums[j] > target) continue

            if (nums[i] + nums[j] == target) {

                return [i, j]

            } else {

                console.log(`i=${nums[i]} j=${nums[j]}`)

            }

        }

    }

}

console.log(targetSumPair(nums,target))

Expected Optimized Way:

function targetSumPair(nums, target) {

    let obj = {};

    for (let i = 0; i < nums.length; i++) {

        let complement = target - nums[i];

        if (obj[complement] !== undefined) {

            return [obj[complement], i];

        }

        obj[nums[i]] = i;

    }

}

console.log(targetSumPair([2, 7, 11, 15], 9));{

 

Javascript:Array insert between the array

Here 16 is missing between 9 & 25 that we need to insert at that very place.

let arr = [1, 4, 9, 25, 36];

arr.splice(3, 0, 16);

console.log(arr);

Output:

    [1, 4, 9, 16, 25, 36]

splice(3, 0, 16) means:

3 → index where to insert

0 → don't remove anything if 1 remove one element,if 2 remove 2 element

16 → value to insert 

Here  Original array is mutated.

let arr = [1, 4, 9, 25, 36];

arr.splice(3, 0, 16,17,18);

console.log(arr);

Output:

   [

   1,  4,  9, 16,

  17, 18, 25, 36

]

splice(3, 0, 16) //means:

3 → index where to insert

0 → don't remove anything if 1 remove one element,if 2 remove 2 element

 16,17,18 → value to insert

Javascript:Array Slice

 

slice do not alter original array,array's some part is copied to destination copying is shallow

let languages = ["java","javascript","Go",{node:"javascript"}]

let firstLanguage = languages.slice(3,4)

firstLanguage[0]["node"] = "python" //this value being object is shallow copied hence changes witll in parent also

console.log(languages)

console.log(firstLanguage)

Output:

[ 'java', 'javascript', 'Go', { node: 'python' } ]

[ { node: 'python' } ]

primitive types are copies by value

Javascript Array:Shift & unshift

 

//shift -alter original array give first element of array after remving from original array

let languages = ["java","javascript","Go"]

let firstLanguage = languages.shift()

console.log(languages)

console.log(firstLanguage)

//unshfit

let cities = ["noida","delhi","pune","nagpur"]//

let new_cities = cities.unshift("mumbai")//return new length of array prior add new element to beginning of array

console.log(cities)

console.log(new_cities)

Output:

PS C:\Users\sangr\Practice> node .\unshift.sh

[ 'javascript', 'Go' ]

java

PS C:\Users\sangr\Practice> node .\unshift.sh

[ 'javascript', 'Go' ]

java

[ 'mumbai', 'noida', 'delhi', 'pune' ]

4

PS C:\Users\sangr\Practice> node .\unshift.sh

[ 'javascript', 'Go' ]

java

[ 'mumbai', 'noida', 'delhi', 'pune', 'nagpur' ]

Mysql:Find employee with same salary in employee table

 

Find employee with same salary from employee table

CREATE TABLE employee (

    id INT AUTO_INCREMENT PRIMARY KEY,

    name VARCHAR(100) NOT NULL,

    age INT,

    city VARCHAR(100),

    salary DECIMAL(10, 2),

    doj DATE

);

INSERT INTO employee (name, age, city, salary, doj)

VALUES

('John', 28, 'Noida', 50000, '2022-06-15'),

('Jerry', 32, 'Delhi', 65000, '2020-03-10'),

('Bill', 25, 'Mumbai', 45000, '2023-01-20'),

('Siara', 30, 'Pune', 70000, '2019-08-05');

INSERT INTO employee (name, age, city, salary, doj)

VALUES

('Amit', 29, 'Delhi', 50000, '2021-04-12'),

('Rahul', 35, 'Noida', 65000, '2018-07-19'),

('Neha', 27, 'Mumbai', 45000, '2022-11-03'),

('Priya', 31, 'Pune', 70000, '2020-02-14'),

('Raj', 26, 'Delhi', 50000, '2023-05-22'),

('Ankit', 33, 'Noida', 75000, '2017-09-11'),

('Sneha', 28, 'Mumbai', 65000, '2021-12-01'),

('Vikas', 37, 'Pune', 80000, '2016-06-18'),

('Pooja', 29, 'Delhi', 75000, '2022-03-25'),

('Karan', 34, 'Noida', 80000, '2019-10-07');

Solution

SELECT salary,JSON_ARRAYAGG(name) AS employee_salary

FROM employee group by salary;

Output:

+----------+-----------------------------+

| salary   | employee_salary             |

+----------+-----------------------------+

| 45000.00 | ["Bill", "Neha"]            |

| 50000.00 | ["John", "Amit", "Raj"]     |

| 65000.00 | ["Jerry", "Rahul", "Sneha"] |

| 70000.00 | ["Siara", "Priya"]          |

| 75000.00 | ["Ankit", "Pooja"]          |

| 80000.00 | ["Vikas", "Karan"]          |

+----------+-----------------------------+

6 rows in set (0.00 sec)

SELECT salary,group_concat(name) AS employee_salary

FROM employee group by salary;

Output:

+----------+-------------------+

| salary   | employee_salary   |

+----------+-------------------+

| 45000.00 | Bill,Neha         |

| 50000.00 | John,Amit,Raj     |

| 65000.00 | Jerry,Rahul,Sneha |

| 70000.00 | Siara,Priya       |

| 75000.00 | Ankit,Pooja       |

| 80000.00 | Vikas,Karan       |

+----------+-------------------+

6 rows in set (0.00 sec)

SELECT salary, JSON_OBJECTAGG(name, city)  FROM employee GROUP BY salary;

Output:

+----------+---------------------------------------------------------+

| salary   | JSON_OBJECTAGG(name, city)                              |

+----------+---------------------------------------------------------+

| 45000.00 | {"Bill": "Mumbai", "Neha": "Mumbai"}                    |

| 50000.00 | {"Raj": "Delhi", "Amit": "Delhi", "John": "Noida"}      |

| 65000.00 | {"Jerry": "Delhi", "Rahul": "Noida", "Sneha": "Mumbai"} |

| 70000.00 | {"Priya": "Pune", "Siara": "Pune"}                      |

| 75000.00 | {"Ankit": "Noida", "Pooja": "Delhi"}                    |

| 80000.00 | {"Karan": "Noida", "Vikas": "Pune"}                     |

+----------+---------------------------------------------------------+

Javascript:Guess output of given code

 

Guess Output of code.

let arr =[1,2,3];

let str="1,2,3";

if(arr==str){

    console.log("Equal")

}else{

    console.log("Not equal")

}

if(arr===str){

    console.log("Equal")

}else{

    console.log("Not equal")

}

if(Object.is(arr,str)){

    console.log("Equal")

}else{

    console.log("Not equal")

}

Output:

Equal

Not equal

Not equal

Note:

   [1,2,3].toString() is "1,2,3"

Javascript:Find nth fibonacci number

 

Find nth fibonacci number.

code:

function fibonacci(n){

   if(n==1 || n==2){

    return 1

   }else{

    return fibonacci(n-1) + fibonacci(n-2)

   }

}

let num = fibonacci(5)

console.log(num)

output:

5

Javascript:Remove falsy values from array

Remove falsy values in array:

Code:

const arr = [1, 0, false, "hello", "", null, undefined, NaN, 5];

const result = arr.filter((item)=>{

    return Boolean(item)

});

console.log(result);

Output:

[ 1, 'hello', 5 ]

 

Javascript:Find the maximum difference between any two elements in an input array

 

Find the maximum difference between any two elements in an input array?

Code:

let arr=[12,13,45,20,56,50,5]

function findMaxDifference(arr) {

   let min=arr[0];

   let max=arr[0];

   for(let i=0;i<arr.length;i++){

      if(min > arr[i]){

        min=arr[i]

      }

      if(max < arr[i]){

        max =arr[i]

      }

   }

   console.log(min,max)

   return max -min

}

let maxDiff = findMaxDifference(arr);

console.log(maxDiff)

Output:

5 56

51

Javascript:Capitalize first and last character in sentence

 

Capitalize first and last character in sentence.

Code:

let sentence = "hello john how do you do"

function firstCharCapital(sentence){

  return sentence.at(0).toUpperCase() + sentence.slice(1)

}

function lastCharCapital(sentence){

   return  sentence.slice(0,sentence.length -1 ) +  sentence.at(sentence.length -1).toUpperCase()

}

let firstCharCapitalized = firstCharCapital(sentence)

console.log(firstCharCapitalized)

let lastCharCapitalized = lastCharCapital(sentence)

console.log(lastCharCapitalized)

Output:

Hello john how do you do

hello john how do you dO

Explanation:I have written two functions to get desired result we can call them one

on other like firstCharCapital(lastCharCapital(sentence))

Javascript:bigint datatype

How to use large number in javascript?

Code:

let num1 =123456777867;

let num2 = 5324152355467563;

console.log(num1 *num2); //6.573026946790237e+26

let num3 =123456777867n;

let num4 = 5324152355467563n;

console.log(num3 *num4); //657302694679023748214828121n

output:

6.573026946790237e+26

657302694679023748214828121n

Explanation:

   when number are large there result is aproximated by default

   you can use n at end to declare it as bigint,bigint can store

   large number,if n is at end of number then it is bigint datatype. 

Javascript:res,end,res.json & res.send

 comapre following method

res.send

 res.json

 res.end

 Answer:

Following table explain difference betweeen 3.

Method       What it does   Content-Type    Ends response?

res.send()  Sends a response and automatically handles common data types    Automatically sets appropriate Content-Type ✅ Yes

res.json()  Sends a JSON response   application/json    ✅ Yes

res.end()   Ends the HTTP response directly Does not automatically set Content-Type ✅ Yes

1. res.send()

    res.send("hello");

    typically results in:

    Content-Type: text/html; charset=utf-8

2. res.json()

res.json({ "using": "json" });

Specifically sends a JSON response and sets:

Content-Type: application/json; charset=utf-8

3. res.end()

res.end("using end");

This directly ends the underlying HTTP response.

It does not provide Express's automatic formatting/content-type behavior like res.send() or res.json().

Javascript:Guess output of given code

 

Guess:

Guess output of following code.

Code:

console.log(NaN === NaN)

const set = new Set([NaN, NaN]);

console.log(set.size);

console.log(Object.is(NaN,NaN))

Output:

false

1

true

Explaination:

    Two NaN are not equal in == comparision but Object.is has them equal.

set size will be 1 because in set consider it unique.

Javascript:Guess Output of given code

 

Code:Guess Output of following code

Code:

const x=[];

x[4] = 1;

x.forEach((item,index,array)=>{

   console.log(`${item} at index = ${index}`);

})

Output:

1 at index = 4

Explaination:

in array x length is 5 but all element from index 0,1,2,3

are not initialized and are defined as empty,foreach loop

only over array element which are not empty hence forEach

will give console.log for only 4th index.

Javascript:Guess output if given code

 

Guess output of following code.

Code:

setTimeout((a,b)=>{

  console.log(a+b)

},1000,1,2,3)

Output:

3

Explanation:

Here 1000 is timeout deplay microseconds while parameters 1,2,3 are

parameter for callback function inside setimeout,inner callback function prints

a+b i.e 1+2 i.e. 3

Javascript:Method Chaiining

Implement method chaining.

Code:

function multiply(x) {

    let multiplication = x;

    return {

        multiply(num) {

            multiplication *= num;

            return this;

        },

        getValue() {

            return multiplication;

        }

    };

}

let result = multiply(1).multiply(5).getValue();

console.log(result);

Output:

5

Javascript:Guess output of given code

 

Guess Output of following code

Code:

function sumNumber(a,b){

    "use strict"

    a=30;

    b=50;

    return arguments[0] + arguments[1];

}

let sum = sumNumber(10,20);

console.log(`sum=${sum}`)

Output:

sum=30

Explanation:

   if we add use strict them we can't override value of

   function parameter inside function.

Javascript:check given number armstrong without string manipulations

 

Check given number is armstrong number.

Code:

let number = 153

function isArmstrong(number){

   let num = number;

   let sum =0

   let length = 0

   let digits =[]

   while(num > 0){

        let digit = num %10;

        num = Math.floor(num /10)

        length ++;

        digits.push(digit)

   }

   sum = digits.reduce((acc,item)=>{

     acc =acc + item ** length

     return acc;

   },0)

   console.log(`sum=${sum}`)

   return sum == number

}

console.log(isArmstrong(number))

Output:

    sum=153

    true

Javascript:Check given number is Armstrong number

 

write code to check given number is armstrong number.

Code:

let number = 153

function isArmstrong(num){

    let expo = num.toString().length;

    let digits = num.toString().split('').map((it)=> Number(it))

    console.log('Exponentional:',expo)

    console.log('Digits:',digits)

    let sum=0;

    for(let i=0;i<digits.length;i++){

       sum=sum + digits[i] ** expo

    }

    return num ==sum

}

console.log(isArmstrong(number))

Output:

true

Javascript:custom filter function to emulate array.filter

Write a custom function to which will emulate array.filter()

Code:

    let arr=[10,2,12,45,8,23];

    function customFilter(arr,callback){

        let result=[];

        for(let i=0;i<arr.length;i++){

            if(callback(arr[i],i,arr)){

                result.push(arr[i])

            }

        }

        return result;

    }

    function lessThan10(num,index,arr){

    if(num > 10){

        return true

    }else{

        return false;

    }

    }

    var filtered = customFilter(arr,lessThan10);

    console.log(filtered)

Output:

[ 12, 45, 23 ] 

Javascript:Build nexted array from given array

 

From given array [1,2,3,4,5] build nexted array [1,[2,[3,[4,[5]]]]]

Code:

    let arr=[1,2,3,4,5]

    function buildNextedArray(arr){

    for(let i=0;i<arr.length;i++){

        if(arr.length==1){

            return [arr[i]]

        }else{

            let newArr = arr.slice(1)

            return [arr[i],buildNextedArray(newArr)]

        }

    }

    }

    let result = buildNextedArray(arr);

    console.log(JSON.stringify(result));

Output:

    [1,[2,[3,[4,[5]]]]]

Javascript:flatten nexted array

 

Flatten nexted array without using flat

Code:

let numbers = [1, [2, [3, 4], 5]]

//console.log(numbers.flat(Infinity)) //uses flat

function flatten(arr,result=[]) {

    for (let item of arr) {

        console.log(item)

        if (Array.isArray(item)) {

            flatten(item,result)

        } else {

            result.push(item)

        }

    }

    return result

}

let flattened = flatten(numbers)

console.log(flattened)

Output:

[ 1, 2, 3, 4, 5 ]

Javascript:Filter using flatMap

In  given array filter positive numbers.

Code :

const arr = [5, -2, 7, -1, 9];

const nonNegative = arr.flatMap((item)=>{

    return (item>0)?[item]:[]

})

//using filter only

//const nonNegative = arr.filter((item)=>item > 0)

console.log(nonNegative)

Output:

[ 5, 7, 9 ]

Javascript:Find all words in array of sentences

find all words in array of sentences.

Code:

const sentences = [

    "I love JavaScript",

    "flatMap is useful"

];

let flattened = sentences.flatMap(item=>item.split(" "))

console.log( flattened)

Output:

[ 'I', 'love', 'JavaScript', 'flatMap', 'is', 'useful' ]

without flatMap same ouput can be obtained by first map then flat

const sentences = [

    "I love JavaScript",

    "flatMap is useful"

];

let flattened = sentences.map(item=>item.split(" ")).flat()

console.log(flattened);

Javascript:filter array for even square

 

filter an array which are even

Code:

let arr = [2, 3, 4, 5, 6, 7];

let result = arr.flatMap((item) => {

    if (item % 2 === 0) {

        return [item * item];

    }

    return [];

});

console.log(result);

Output:

[4, 16, 36]

Explanation:

  flatMap is combination of filter & map.If no value is to be

returned is empty array & return value shoulld be put i array syntax.