foldArray.js with dry run ( ***REVISE***)

 /*Fold Array

You are given an array of size n. Imagine the array as a length of rope.

You have to fold the rope at the middle. You are also given an input integer

numOfFolds that specifies the number of times you should fold your array.

To illustrate more, say the given array is 1,4,9.

Folding it in the middle results in 10, 4 as 9 and 1 get combined by the fold.

Say the given array is 1,10,20,21,2. Folding it would lead to: 3, 31, 20 as 2, 1

have combined and 10, 21 have combined.

Based on the numOfFolds repeat folding.

Input.

The first line contains n, the number of elements in the array.

This is followed by n lines, each containing one integer

The last line contains m, the number of folds to do.

Output

The first line contains k, the number of elements in the final array

This is followed by k lines, each containing one integer element of the output array

Example

Odd length array

Input:

5

-1

4

2

3

1

1

Output:

3

0

7

2

Even length array

Input:

6

3

1

6

7

2

3

1

Output:

3

6

3

13

Explanation

Odd number n

The first line contains 5 indicating 5 elements in the input array

The next 5 lines contain the array elements: -1, 4, 2, 3, 1

The last line contains 1 indicating one fold to be made

The first and last element merge: -1 + 1 = 0

The second and 4th element merge: 4 + 3 = 7

The middle element is 2. It remains unchanged because of the fold

So the result is 0, 7, 2

Even number n

The first line contains 6 indicating 6 elements in the input array

The next 6 lines contain the array elements: 3, 1, 6, 7, 2, 3

The last line contains 1 indicating one fold to be made

The first and last element merge: 3 + 3 = 6

The second and 5th element merge: 1 + 2 = 3

The third and 4th element merge: 6 + 7 = 13

So the result is 6, 3, 13

*/

let fs = require("fs");

let data = fs.readFileSync(0, 'utf-8');

let idx = 0;

data = data.split('\n');

function readLine() {

idx++;

return data[idx - 1].trim();

}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////

// This part is for taking the input in array format only

const noOfElementsInArray = parseInt(readLine()); // 5

let arr = [] // we will push the elements in this empty array

for (let i = 0; i < noOfElementsInArray; i++) {

// arr[i] = parseInt(readLine());

arr.push(parseInt(readLine()));

// or arr[i] = parseInt(readLine()); both will give the same result

// console.log(arr)

// [ -1 ] when i=0

// [ -1, 4 ] when i=1

// [ -1, 4, 2 ] when i=1

// [ -1, 4, 2, 3 ] when i=2

// [ -1, 4, 2, 3, 1 ]when i=3

// [ -1, 4, 2, 3, 1 ]when i=4 , all yellow color elements

}

const noOfFolds = parseInt(readLine()); // 1

for (let folds = 0; folds < noOfFolds; folds++) // 0) folds =0<1 true go inside the forloop

// 2) folds =1<1 false , exit the forloop

completely and go to the console statements

we came to fols = 1 after breaking and

exiting from the inner while loop

{

// for each fold

let i = 0; // initialization for while loop

while (i < arr.length) // 0) i=0 <5 true, go inside the while loop

// 1) i=1<5 true, go inside the while loop

// 2) i=2<5 true , go inside the while loop

{

if (i == arr.length - 1) // 0) i=0 == 4 (5-1) false don't go inside if condition

// 1) i=1 == 3 (4-1)false don't go inside if condition

// 2) i=2 == 2 (3-1)true , now break from this while loop

completely and go for folds++ i.e., folds = 1 in the

main forloop

{

break;

}

let lastElement = arr[arr.length - 1]; // 0) lastElement = arr[4] = 1

the arr is [-1, 4, 2, 3, 1]

// 1) lastElement = arr[3] = 3

the arr is [0,4,2,3]

arr[i] += lastElement; // 0) arr[0] = arr[0] + lastElement i.e., arr[0] = -1+1 = 0

now the arr = [0, 4, 2, 3, 1]

// 1) arr[1] = arr[1] + lastElement i.e., arr[1] = 4+ 3 =7

now the arr = [0,7,2,]

i++; // 0) i++ now i is 1

// 1) i++ now i is 2

arr.pop(); // 0) 1 will be removed from the back of arr array and now continue with

while loop of i=1

and the arr after pop will be arr =[0,4,2,3]

// 1) 3 will be removed from the back of arr array and now continue with

while loop of i=2

and the arr after pop this time will be arr =[0,7,2]

}

}

//console.log(arr) [ 0, 7, 2 ] yellow color elements

console.log(arr.length); // 3 this statement is executed only after exiting the top main

forloop.

for (let i = 0; i < arr.length; i++) // 0) i=0<3 true ,go inside forloop , this statement is

executed only after exiting the top main forloop

1) i=1<3 true, go inside forloop

2) i=2<3 true, go inside forloop

3) i=3<3 false , exit the forloop completely

{

console.log(arr[i]); // 0) arr[0] = 0 , i++ now i=1

// 1) arr[1] = 7 , i++ now i=2

// 2) arr[2] = 2 , i++ now i=3

}

//////////////////////////////////////////////////////////////////////////////////////////////

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