Same boat here bro. Been learning JavaScript for months now haha
Hi,
This is the solution from the book:
// I can’t figure this one out. Can someone please explain:
in the loop why is the condition set to 2? Loop is programmed to stop when it reaches 2 is what I see. Is this right?
// also the variable old - I don’t understand the purpose of this variable, it doesn’t seem necessary.
function reverseArrayInPlace(array) {
for (let i = 0; i < Math.floor(array.length / 2); i++) {
let old = array[i];
array[i] = array[array.length - 1 - i];
array[array.length - 1 - i] = old;
}
return array;
}
let arrayValue = [1, 2, 3, 4, 5];
reverseArrayInPlace(arrayValue);
console.log(arrayValue);
// → [5, 4, 3, 2, 1];
// RANGE FUNCTION – range(1,40,-2); //[40, 38, 36, 34, 32, 30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2]
function range(x,y,z){
let array = [], maxValue=y;
if(z<0) {y=x;x=maxValue;}; // swap values if descending array
for(let i=0;i<Math.abs(maxValue/z);i++){
array[i] = x;
x+=z;
}
return array;
}
// SUM FUNCTION – sum(range(1,5,1)); //15
function sum(array){
let sum = 0;
for(let i=0;i<array.length;i++){
sum+=array[i];
}
return sum;
}
//REVERSE – reverseArray(range(1,20,-2)); //[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
function reverseArray(array){
let reversedArray = [];
let x = array.length-1;
for(let i=0; i<array.length;i++){
reversedArray[i] = array[x];
x–;
}
return reversedArray;
}
//REVERSE IN PLACE --myArray-range(1,20,2); reverseArrayInPlace(myArray); //[19, 17, 15, 13, 11, 9, 7, 5, 3, 1]
function reverseArrayInPlace(array){
let x = array.length-1;
for (let i=0;i<parseInt(array.length/2);i++){
let tmp = array[i];
array[i] = array[x];
array[x] = tmp;
x–;
}
return array; // return for convenience
}
1 Like
The sum of a range
- a) function range(start, end) {
var result = [ ];
for ( let y = start; y <= end; y++)
{ result.push(y); }
return result; }
console.log( range(1,10) );
b) function sum(total,count)
{var total = 0, count = 1;
while (count <= 10)
{total += count;
count ++;}
return total; };
console.log(sum(1,10));
- a) function range(start,end,step) {
var result = [ ];
for (let y= start; y< end; y+=step)
{ result.push(y) ; }
return result ; };
console.log( range(1,10,2) );
b) function range(start,end,step)
{ var result = [ ];
for (var y=start; y>=end; y+=step)
{ result.push(y) }
return result ; };
console.log( range(5,2,-1) );
Reversing an array
-
function reverseArray()
{var reverseArray=[1,5,7,9].reverse( ); return reverseArray ; } ;
console.log( reverseArray( ) ); -
function reverseArrayInPlace(array)
{ var result = [ ];
for (var y = array.length - 1; y >= 0; y–)
{ result.push(array[y]) ; }
return result ; };
console.log(reverseArrayInPlace( [2,4,7,9] ) );
1 Like
Here is my solution.
<script type="text/javascript">
//the sum of a range
let range = function (start, end, step=1){
output=[];
if(start<end){
for(let number=start; number<=end; number+=step){
output.push(number);
}
}
else if(start>end){
for(let number=start; number>=end; number+=step){
output.push(number);
}
}
return output;
};
let computeSum = function(numbers){
output=0;
for(let iter=0; iter<numbers.length; iter++){
output+=Number(numbers[iter]);
}
return output;
}
//reversing an array
let reverseArray = function(givenArray){
let output=[]
for(let i=givenArray.length-1; i>=0; i-=1){
output.push(givenArray[i])
}
return output;
}
let reverseArrayInPlace = function(givenArray){
let temp=[];
for(i=0;i<givenArray.length;i++){
temp[i]=givenArray[i];
}
for(i=0; i<givenArray.length; i++){
givenArray[i]=temp[givenArray.length-1-i];
}
}
</script>
The sum of a range:
var range = function(start, end) {
var array = [];
cnt = start;
while (cnt <= end) {
array.push(cnt);
cnt++;
}
return array;
};
// example 1
var sum = function(array) {
var total = 0;
while(array.length > 0) {
total = total + array.pop();
}
return total;
};
// example 2
var sum2 = function(array) {
var total = 0;
for (let i = 0; i < array.length; i++) {
total = total + array[i];
}
return total;
};
console.log(sum(range(1, 10)));
console.log(sum(range(1, 10)));
1 Like
Reversing an array
const reverseArray = function(array) {
let newArray = [];
array.forEach( (item) => newArray.unshift(item))
return newArray;
}
const answer = reverseArray([1, 2, 3]);
var reverseArrayInPlace = function(array) {
var left = 0;
var length = array.length;
while(left < length) {
array.push(array[length - 1 - ++left]);
array.splice(length - 1 - left, 1);
}
return array;
}
var secondAnswer = reverseArrayInPlace([1,2,3, 4]);
console.log(secondAnswer);
1 Like
hello. Did you figure it out? I don’t get it either
Where should i put an array of numbers to check if it runs_?
(array) ???
Hi, know, and I can’t remember this one anymore. The theory is confusing, I would like more practice personally.
1 Like
I was able to get the first two parts of the first question to work, but had to look to the answer to see how the step might work.
// Q1 Part 1: Prints the range input from "console.log(range(1, 10));"
var range = function (start, end){
var array = [],
counter = start;
while (counter <= end){
array.push(counter);
counter++;
}
return array;
};
console.log(range(1, 10));
// Part 2 -------------------------------------------->
function sum(array){
var total = 0;
for ( var i = 0; i < array.length; i ++ )
total += array[i];
return total;
};
console.log(sum(range(1, 10)));
_______________-
1 Like
// Ch4_Q2_A - Doesn't change array [non mutating]
// creates temp version and reverses it, hence original array remains unchanged
function reverseArray(array) {
let output = [];
for (let i = array.length - 1; i >= 0; i--) {
output.push(array[i]);
}
return output;
}
array = ['a','b','c','d','e']
console.log(array);
console.log(reverseArray(array));
console.log(array);
// Ch4_Q2_B - Changes array by flipping in place [mutates]
function reverseArrayInPlace(array) {
for (let i = 0; i < Math.floor(array.length / 2); i++) {
let old = array[i];
array[i] = array[array.length - 1 - i];
array[array.length - 1 - i] = old;
}
return array;
}
array = ['a','b','c','d','e']
console.log(array);
console.log(reverseArrayInPlace(array));
console.log(array);
1 Like
The sum of a range:
function range(start, end) {
var result = [ ];
for ( let y = start; y <= end; y++)
{ result.push(y); }
return result; }
console.log( range(1,10) );
function sum(total,count)
{var total = 0, count = 1;
while (count <= 10)
{total += count;
count ++;}
return total; };
console.log(sum(1,10));
//IT DOES RETURN 55
Reversing an Array:
function reverseArray()
{var reverseArray=[1,2,3,4].reverse( ); return reverseArray ; } ;
console.log( reverseArray( ) );
1 Like
THE SUM OF RANGE
function rangeArray(min, max, step = 1){
var array = [];
if(min < max){
for(var i = min; i < max+1; i = i + Math.abs(step)){
array.push(i);
}
}
else if(min > max){
for(var i = min; i > max - 1; i = i - Math.abs(step)){
array.push(i);
}
}
return array;
}
console.log(rangeArray(5,2,1));
function sum(arr){
var totalSum = 0;
for(var i = 0; i <arr.length;i++){
totalSum += arr[i];
}
return totalSum;
}
console.log(sum(rangeArray(1, 10)));
REVERSING AN ARRAY
var array = [1, 2, 3, 4, 5, 6];
function reverseArray(arr){
var newArr = [];
for(var i = arr.length; i > -1; i--){
newArr.push(arr[i]);
}
newArr.shift();
return newArr;
}
function reverseInPlace(arr){
var count = arr.length -1;
for(var i = 0; i < (arr.length/2); i++){
var num1= arr[i];
var num2= arr[count];
arr[i] = swapValues(num1, num2);
arr[count] = swapValues(num2, num1);
count--;
}
return arr;
}
function swapValues(a,b){
var c = a;
a=b;
b=c;
return a;
}
console.log("ReverseArray function: " + reverseArray(array));
console.log("ReverseInPlace function: " + reverseInPlace(array));
1 Like
1 -
function range (start, end) {
var array = [];
for (let i = start; i <= end; i+= step) {
array.push(i);
}
return array;
}
console.log(range(1,10));
function sum (array) {
let total = 0;
for (let value of array) {
total += value;
}
return total;
}
console.log(sum(range(1,10)));
2 -
function range (start, end, step) {
let array = [];
if (start < end && step == undefined) {step = 1}
else if (start > end && step == undefined) {step = -1}
if (step > 0) {
for (let i = 0; i <= end; i += step)
array.push(i);
}
else {
for (let i = 0; i >= end; i+= step)
array.push(i);
}
return array;
}
console.log(range(1,10,2);
3 -
function reverseArray = (array) {
let reverseArray = [];
for (let i = 0; i < array.length; i++) {
reverseArray.unshift (array [i]);
}
return reverseArray;
}
console.log(reverseArray([1, 2, 3]);
4 -
function reverseArrayInPlace (array) {
for (let i = 0; i < Math.floor (array.length / 2); i++) {
let temp = array [i];
array [i] = array [array.length -1 -i];
array [array.length -1 -i] = temp;
}
return array;
}
let arrayValue = [1, 2, 3, 4, 5];
reverseArrayInPlace (arrayValue);
console.log(arrayValue);
** Had to look the answer for this last question up, very good problem, had me totally stuck! **
1 Like
//the sum of range
function range(start, end){
let array = [ ];
for (let i = start; i <= end; i++){
array.push(i);
}
return array;
}
console.log(range(-1,10));
//reversing an array
function reverseArray(array){
var result = [];
for(var i = array.length - 1; i >= 0; i--){
result.push(array[i]);
}
return solution;
}
//reverseArrayInPlace
function reverseArrayInPlace(array){
for(var i = 0; i < Math.floor(array.length/2); i++){
var current = array[i];
array[i] = array[array.length - 1 - i];
array[array.length - 1 - i] = current;
}
return array;
}
var arrayValue = [1,2,3,4,5];
reverseArrayInPlace(arrayValue);
console.log(arrayValue);
2 Likes
- The sum of a range:
function range(start, end){
var field = [];
cnt = start;
while (cnt <= end){
field.push(cnt);
cnt++;
}
return field;
};
function sum(arr){
var total = 0;
while(arr.length > 0){
total = total + arr.pop();
}
return total;
};
Here is another way to do it :
function range2(start, end){
var arr = [],
cnt = start;
function increaseCnt(cnt) {
if (cnt >= end){
return arr.push(end);
} else {
arr.push(cnt);
increaseCnt(++cnt);
}
};
increaseCnt(cnt);
return arr;
};
function sum3(arr) {
return arr.reduce(function(tot, val) {
return tot + val;
});
};
console.log(sum3(range2(1, 10)));
Reversing an array:
var arr = [1, 2, 3, 4, 5]
var arr2 = [];
function reverse(arr) {
while (arr.length > 0) {
arr2.push(arr.pop());
}
return arr2;
};
function reverse2(arr1){
let temp
for(let i = 0; i <arr1.length / 2; i++) {
temp = arr1[i]
arr1[i] = arr1[arr1.length - 1 - i]
arr1[arr1.length - 1 - i] = temp
}
return arr1
}
2 Likes
1. The sum of a range.
function range(start, end, step){
let array = [];
for (let x = start; x<=end; x+=step){
array.push(x);
}
return array;
}
console.log(range(1,10,2));
function sum (array) {
let total = 0;
for (let value of array) {
total += value;
}
return total;
}
console.log(sum(range(1,10,2)));
returns [1, 3, 5, 7, 9] and sum of 25
2. Reversing an array
function range(start, end){
let array = [];
for (let x = end; x>=start; x–){
array.push(x);
}
return array;
}
console.log(range(1,10));
2 Likes
Thank you! really like your solution 
function reverseArrayInPlace(array) {
for (let i = 0; i < Math.floor(array.length / 2) ; i++) {
let old = array[i];
array[i] = array[array.length - 1 - i];
array[array.length - 1 - i] = old;
}
return array;
}
let arrayValue = [1, 2, 3, 4, 5];
reverseArrayInPlace(arrayValue);
console.log(arrayValue);
// → [5, 4, 3, 2, 1];
1 Like