Develop Reference

Swapping array Indices

I am trying to find the maximum of a number by swapping two digits. I have written the correct logic and it is getting to the part where I need to swap however after the swap i return the result and it isn't swapping?
var maximumSwap = function(num) {
let str = num.toString()
let left = 0
let right = 1
while (left !== str.length) {
if (parseInt(str[left]) < parseInt(str[right])) {
console.log(str[left], str[right])
let temp = str[left];
str[left] = str[right];
str[right] = temp;
return str
} else if (parseInt(str[left]) > parseInt(str[right])) {
if (left === right) {
left++
right = left + 1
} else if (left < right) {
right++
}
}
}
};
maximumSwap(2736)
// Input: 2736
// Output: 7236
// Explanation: Swap the number 2 and the number 7.

String are immutable in JS. Even though you are changing characters at left and right position, it wont reflect in "str".
Use this link on how to replace characters:
How do I replace a character at a particular index in JavaScript?
Also, your logic is incorrect, if the first position element is largest, loop will run infinite times.

// u can convert the num to string array to exchange
const str = num.toString().split('')
there is an example
// Input: 2736
// Output: 7632
var maximumSwap = function(num) {
let str = num.toString().split('')
let left = 0
let right = 1
while (left < str.length - 1) {
while(right < str.length) {
if (parseInt(str[left]) < parseInt(str[right])) {
// exchange
[str[left], str[right]] = [str[right], str[left]]
}
right++
}
left++
right = left
}
return str.join('')
};

Count how many times a character happens in a string and store it in an array JavaScript

I've been trying to figure out how to count how many times a character happens in a string and store it in another variable that will hold the character and the number of times it occurs in the string.
For example:
var greeting = "Hello World";
[H] occurs [1] time.
[e] occurs [1] time.
[l] occurs [3] times.
[o] occurs [2] times.
[W] occurs [1] time.
[r] occurs [1] time.
[d] occurs [1] time.
I am a JS Beginner and I tried as much as I can following guides and tutorials but this exercise seems to be out of my league. I would appreciate some help as to how would you guys go on about solving this problem.
Thanks!

You basically want to create a mapped set of characters to it's count in the string. Storing this stuff in an array might be weird as you'd need 2 Dimentional arrays. Instead store it in an hash object.
var greeting = "Hello world!";
var hash = {};
for(var i = 0; i < greeting.length; i++){
if(hash[greeting[i]] === undefined){
hash[greeting[i]] = 1;
} else {
hash[greeting[i]] += 1;
}
}
// printing the stuff in hash.
for(var x in hash){
if(hash.hasOwnProperty(x)){
console.log(x, hash[x]);
}
}
Anyway if you need this stuff in array, you can put so:
var arr = [];
var i = 0;
for(var x in hash){
if(hash.hasOwnProperty(x)){
arr[i++] = [x, hash[x]];
}
}
for(var i = 0; i< arr.length; i++){
console.log(arr[i]);
}
But I wouldn't recommend it. You can see redundancy for yourself.

Try this:
var result = {};
Array.prototype.map.call('Hello world!', function(x) {
if (typeof result[x] == 'undefined') {
result[x] = 1;
} else {
result[x] += 1;
}
});
console.log(result);
var result = {};
Array.prototype.map.call('Hello world!', function(x) {
if (typeof result[x] == 'undefined') {
result[x] = 1;
} else {
result[x] += 1;
}
});
console.log(result);

"Look and say sequence" in javascript

1
11
12
1121
122111
112213
122211
....
I was trying to solve this problem. It goes like this.
I need to check the former line and write: the number and how many time it was repeated.
ex. 1 -> 1(number)1(time)
var antsArr = [[1]];
var n = 10;
for (var row = 1; row < n; row++) {
var lastCheckedNumber = 0;
var count = 1;
antsArr[row] = [];
for (var col = 0; col < antsArr[row-1].length; col++) {
if (lastCheckedNumber == 0) {
lastCheckedNumber = 1;
antsArr[row].push(lastCheckedNumber);
} else {
if (antsArr[row-1][col] == lastCheckedNumber) {
count++;
} else {
lastCheckedNumber = antsArr[row-1][col];
}
}
}
antsArr[row].push(count);
antsArr[row].push(lastCheckedNumber);
}
for (var i = 0; i < antsArr.length; i++) {
console.log(antsArr[i]);
}
I have been on this since 2 days ago.
It it so hard to solve by myself. I know it is really basic code to you guys.
But still if someone who has a really warm heart help me out, I will be so happy! :>

Try this:
JSFiddle Sample
function lookAndSay(seq){
var prev = seq[0];
var freq = 0;
var output = [];
seq.forEach(function(s){
if (s==prev){
freq++;
}
else{
output.push(prev);
output.push(freq);
prev = s;
freq = 1;
}
});
output.push(prev);
output.push(freq);
console.log(output);
return output;
}
// Sample: try on the first 11 sequences
var seq = [1];
for (var n=0; n<11; n++){
seq = lookAndSay(seq);
}
Quick explanation
The input sequence is a simple array containing all numbers in the sequence. The function iterates through the element in the sequence, count the frequency of the current occurring number. When it encounters a new number, it pushes the previously occurring number along with the frequency to the output.
Keep the iteration goes until it reaches the end, make sure the last occurring number and the frequency are added to the output and that's it.

I am not sure if this is right,as i didnt know about this sequence before.Please check and let me know if it works.
var hh=0;
function ls(j,j1)
{
var l1=j.length;
var fer=j.split('');
var str='';
var counter=1;
for(var t=0;t<fer.length;t++)
{
if(fer[t]==fer[t+1])
{
counter++;
}
else
{
str=str+""+""+fer[t]+counter;
counter=1;
}
}
console.log(str);
while(hh<5) //REPLACE THE NUMBER HERE TO CHANGE NUMBER OF COUNTS!
{
hh++;
//console.log(hh);
ls(str);
}
}
ls("1");

You can check out the working solution for in this fiddle here
You can solve this by splitting your logic into different modules.
So primarily you have 2 tasks -
For a give sequence of numbers(say [1,1,2]), you need to find the frequency distribution - something like - [1,2,2,1] which is the main logic.
Keep generating new distribution lists until a given number(say n).
So split them into 2 different functions and test them independently.
For task 1, code would look something like this -
/*
This takes an input [1,1,2] and return is freq - [1,2,2,1]
*/
function find_num_freq(arr){
var freq_list = [];
var val = arr[0];
var freq = 1;
for(i=1; i<arr.length; i++){
var curr_val = arr[i];
if(curr_val === val){
freq += 1;
}else{
//Add the values to the freq_list
freq_list.push([val, freq]);
val = curr_val;
freq = 1;
}
}
freq_list.push([val, freq]);
return freq_list;
}
For task 2, it keeps calling the above function for each line of results.
It's code would look something like this -
function look_n_say(n){
//Starting number
var seed = 1;
var antsArr = [[seed]];
for(var i = 0; i < n; i++){
var content = antsArr[i];
var freq_list = find_num_freq(content);
//freq_list give an array of [[ele, freq],[ele,freq]...]
//Flatten so that it's of the form - [ele,freq,ele,freq]
var freq_list_flat = flatten_list(freq_list);
antsArr.push(freq_list_flat);
}
return antsArr;
}
/**
This is used for flattening a list.
Eg - [[1],[1,1],[1,2]] => [1,1,1,1,2]
basically removes only first level nesting
**/
function flatten_list(li){
var flat_li = [];
li.forEach(
function(val){
for(ind in val){
flat_li.push(val[ind]);
}
}
);
return flat_li;
}
The output of this for the first 10 n values -
OUTPUT
n = 1:
[[1],[1,1]]
n = 2:
[[1],[1,1],[1,2]]
n = 3:
[[1],[1,1],[1,2],[1,1,2,1]]
n = 4:
[[1],[1,1],[1,2],[1,1,2,1],[1,2,2,1,1,1]]
n = 5:
[[1],[1,1],[1,2],[1,1,2,1],[1,2,2,1,1,1],[1,1,2,2,1,3]]
n = 6:
[[1],[1,1],[1,2],[1,1,2,1],[1,2,2,1,1,1],[1,1,2,2,1,3],[1,2,2,2,1,1,3,1]]
n = 7:
[[1],[1,1],[1,2],[1,1,2,1],[1,2,2,1,1,1],[1,1,2,2,1,3],[1,2,2,2,1,1,3,1],[1,1,2,3,1,2,3,1,1,1]]
n = 8:
[[1],[1,1],[1,2],[1,1,2,1],[1,2,2,1,1,1],[1,1,2,2,1,3],[1,2,2,2,1,1,3,1],[1,1,2,3,1,2,3,1,1,1],[1,2,2,1,3,1,1,1,2,1,3,1,1,3]]
n = 9:
[[1],[1,1],[1,2],[1,1,2,1],[1,2,2,1,1,1],[1,1,2,2,1,3],[1,2,2,2,1,1,3,1],[1,1,2,3,1,2,3,1,1,1],[1,2,2,1,3,1,1,1,2,1,3,1,1,3],[1,1,2,2,1,1,3,1,1,3,2,1,1,1,3,1,1,2,3,1]]

for loop not executing properly Javascript

i m trying to calculate weight of a string using the following function
function weight(w)
{
Cap = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
small = 'abcdefghijklmnopqrstuvwxyz'
spcl = "~!##$%^&*()_+[]\{}|;':,./<>?"
num = '0123456789'
var p = []
for(i=0;i<w.length;i++)
{
if(Cap.contains(w[i])==true)
p[i] = Cap.indexOf(w[i]) + 2
else if(small.contains(w[i])==true)
p[i] = small.indexOf(w[i]) + 1
else if(num.contains(w[i]))
p[i] = num.indexOf(w[i])
else if(spcl.contains(w[i]))
p[i] = 1
}
return _.reduce(p,function(memo, num){ return memo + num; }, 0);
}
where w is a string. this properly calculates weight of the string.
But whn i try to to calculate weight of strings given in a an array, it jst calculates the weight of the first element, ie. it does not run the full for loop. can anyone explain to me why is that so??
the for loop is as given below
function weightList(l)
{
weigh = []
for(i=0;i<l.length;i++)
weigh.push(weight(l[i]));
return weigh;
}
input and output:
>>> q = ['abad','rewfd']
["abad", "rewfd"]
>>> weightList(q)
[8]
whereas the output array should have had 2 entries.
[8,56]
i do not want to use Jquery. i want to use Vanilla only.

Because i is a global variable. So when it goes into the function weight it sets the value of i greater than the lenght of l. Use var, it is not optional.
for(var i=0;i<l.length;i++)
and
for(var i=0;i<w.length;i++)
You should be using var with the other variables in the function and you should be using semicolons.

I think your issue is just malformed JavaScript. Keep in mind that JavaScript sucks, and is not as forgiving as some other languages are.
Just by adding a few "var" and semicolons, I was able to get it to work with what you had.
http://jsfiddle.net/3D5Br/
function weight(w) {
var Cap = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
small = 'abcdefghijklmnopqrstuvwxyz',
spcl = "~!##$%^&*()_+[]\{}|;':,./<>?",
num = '0123456789',
p = [];
for(var i=0;i<w.length;i++){
if(Cap.contains(w[i])==true)
p[i] = Cap.indexOf(w[i]) + 2
else if(small.contains(w[i])==true)
p[i] = small.indexOf(w[i]) + 1
else if(num.contains(w[i]))
p[i] = num.indexOf(w[i])
else if(spcl.contains(w[i]))
p[i] = 1
}
return _.reduce(p,function(memo, num){ return memo + num; }, 0);
}
function weightList(l) {
var weigh = [];
for(var i=0;i<l.length;i++)
weigh.push(weight(l[i]));
return weigh;
}
q = ['abad','rewfd'];
results = weightList(q);
Hope that helps

Javascript: Example of recursive function using for loops and substring - can't figure out where I'm going wrong

I'm currently working on coderbyte's medium challenge entitled "Permutation Step."
The goal is to take user input, num, and to return the next number greater than num using the same digits So, for example, if user input is 123, then the number 132 should be returned. If user input is 12453, then 12534 should be returned...
Anywho, I have a correct model answer created by someone (probably a genius, cuz this stuff is pretty hard) and I'm trying to figure out how the answer works, line for line by having an example play out (I'm keeping it simple and playing out the function with user input 123).
The answer has 2 functions, but the 1st function used is what I'm currently trying to work out...
The relevant code is:
var PermutationStep1 = function(num) {
var num1 = num.toString();
var ar = [];
//return num1;
if (num1.length < 2) {
return num;
} else {
for(var i = 0; i < num1.length; i++) {
var num2 = num1[i];
var num3 = num1.substr(0,i) + num1.substr(i+1, num1.length -1);
var numAr = PermutationStep1(num3);
for(var j = 0; j < numAr.length; j++) {
ar.push(numAr[j] + num2);
}
}
ar.sort(function(a,b) {return a-b});
return ar;
}
}
Again, I'm trying to work thru this function with the inputted num as 123 (num = 123).
I'm pretty sure that this function should output an array with multiple elements, because the 2nd function merely compares those array elements with the original user input (in our case, 123), and returns the next greatest value.
So in our case, we should probably get an array, named 'ar', returned with a host of 3 digit values. But for some reason, I'm getting an array of 2 digit values. I can't seem to isolate my mistake and where I'm going wrong. Any help with where, specifically, I'm going wrong (whether it be the recursion, the use of substring-method, or the concating of strings together, whatever my problem may be) would be appreciated...
Here's some of my work so far:
PS1(123) / num1 = 123
i = 0;
num2 = (num1[i]) = '1';
num3 = (num1.substr(0, 0) + num1.substr(1, 2)) = ('0' + '23') = '23'
PS1(23)
i = 0;
num2 = '2';
num3 = '3'
PS1(3) -> numAr = 3 (since num1 is less than 2 digits, which is the recursion base case?)
(So take 3 into the 2nd for loop)...
ar.push(numAr[j] + num2) = ar.push('3' + '1') = 31
ar = [31] at this point
And then I go through the initial for-loop a couple more times, where i = 1 and then i = 2, and I eventually get....
ar = [31, 32, 33]...
But I'm thinking I should have something like ar = [131, 132, 133]? I'm not sure where I'm going wrong so please help. Because the answer is correctly spit out by this function, the correct answer being 132.
Note: if you need the 2nd part of the model answer (i.e. the 2nd function), here it is:
var arr = [];
function PermutationStep(num1) {
arr.push(PermutationStep1(num1));
var arrStr = arr.toString();
var arrStrSpl = arrStr.split(",");
//return arrStrSpl;
for(var p = 0; p < arrStrSpl.length; p++) {
if(arrStrSpl[p] > num1) {
return arrStrSpl[p];
}
}
return -1;
}

I'm sorry the first function i posted was under a mathematical logical mistake and i was to overhasty
I thought about it again and now i have the following function which definitley works
function getNextNumber (num)
{
var numberStr=num.toString (), l=numberStr.length, i;
var digits=new Array (), lighterDigits, digitAtWeight;
var weight,lightWeight, lighterDigits_l, value=0;
for (i=l-1;i>-1;i--)
digits.push (parseInt(numberStr.charAt(i)));
lighterDigits=new Array ();
lighterDigits.push (digits[0]);
for (weight=1;weight<l;weight++)
{
digitAtWeight=digits[weight];
lighterDigits_l=lighterDigits.length;
for (lightWeight=0;lightWeight<lighterDigits_l;lightWeight++)
{
if (digitAtWeight<lighterDigits[lightWeight])
{
lighterDigits.unshift (lighterDigits.splice (lightWeight,1,digitAtWeight)[0]);
lighterDigits.reverse ();
digits=lighterDigits.concat (digits.slice (weight+1,l));
for (weight=0;weight>l;weight++)
value+=Math.pow (10,weight)*digits[weight];
return value;
}
}
lighterDigits.push (digitAtWeight);
}
return NaN;
}

okay here is my solution i found it in 20 minutes ;)
//---- num should be a Number Object and not a String
function getNextNumber (num)
{
var numberStr=num.toString (), l=numberStr.length, i;
var digits=new Array (), digitA, digitB;
var weight,lightWeight;
var valueDifference,biggerValue;
for (i=l-1;i>-1;i--)
digits.push (parseInt(numberStr.charAt(i))); // 345 becomes a0=5 a1=4 a2=3 and we can say that num= a0*10^0+ a1*10^1+ a2*10^2, so the index becomes the decimal weight
for (weight=1;weight<l;weight++)
{
digitA=digits[weight];
biggerValue=new Array ();
for (lightWeight=weight-1;lightWeight>-1;lightWeight--)
{
digitB=digits[lightWeight];
if (digitB==digitA) continue;
valueDifference=(digitA-digitB)*(-Math.pow(10,weight)+Math.pow (10,lightWeight));
if (valueDifference>0) biggerValue.push(valueDifference);
}
if (biggerValue.length>0)
{
biggerValue.sort();
return (biggerValue[0]+num);
}
}
}

this is the solution I figured out for the problem without using a recursive function. It's passed all the tests on coderbyte. I am still new to this so using recursion is not the first thing I look for. hope this can help anyone else looking for a solution.
function PermutationStep(num) {
var numArr = (num + '').split('').sort().reverse();
var numJoin = numArr.join('');
for (var i = (num + 1); i <= parseInt(numJoin); i++){
var aaa = (i + '').split('').sort().reverse();
if (aaa.join('') == numJoin){
return i;
}
}
return -1;
}