# freeCodeCamp Algorithm Challenge Guide: Search and Replace

freeCodeCamp Algorithm Challenge Guide: Search and Replace
0

#1

Remember to use `Read-Search-Ask` if you get stuck. Try to pair program and write your own code

### Problem Explanation:

You will create a program that takes a sentence, then search for a word in it and replaces it for a new one while preserving the uppercase if there is one.

## Hint: 1

• Find the index where `before` is in the string.

try to solve the problem now

## Hint: 2

• Check first letter case.

try to solve the problem now

## Hint: 3

• Strings are immutable, you will need to save the edits on another variable, even if you must reuse the same one just to make it look like the changes where done using just that one variable.

try to solve the problem now

## Basic Code Solution:

``````function myReplace(str, before, after) {
// Find index where before is on string
var index = str.indexOf(before);
// Check to see if the first letter is uppercase or not
if (str[index] === str[index].toUpperCase()) {
// Change the after word to be capitalized before we use it.
after = after.charAt(0).toUpperCase() + after.slice(1);
}
// Now replace the original str with the edited one.
str = str.replace(before, after);

return str;
}

// test here
myReplace("A quick brown fox jumped over the lazy dog", "jumped", "leaped");
``````

### Code Explanation:

• Use `indexOf()` to find location of before in string.
• If first letter of before is capitalized, change first letter of after to uppercase.
• Replace before in the string with after.
• Return the new string.

## Intermediate Code Solution:

``````function myReplace(str, before, after) {
//Create a regular expression object
var re = new RegExp(before,"gi");
//Check whether the first letter is uppercase or not
if(/[A-Z]/.test(before[0])){
//Change the word to be capitalized
after = after.charAt(0).toUpperCase()+after.slice(1);
}
//Replace the original word with new one
var  newStr =  str.replace(re,after);

return newStr;
}

// test here
myReplace("A quick brown fox jumped over the lazy dog", "jumped", "leaped");
``````

### Code Explanation:

• In this solution, regular expression `[A-Z]` is used to check if character is uppercase.
• Create a new regular expression object, re.
• If first letter of before is capitalized, change the first letter of after to uppercase.
• Replace before with after in the string.
• Return the new string.

``````function myReplace(str, before, after) {

// create a function that will change the casing of any number of letter in parameter "target"
// matching parameter "source"
function applyCasing(source, target) {
// split the source and target strings to array of letters
var targetArr = target.split("");
var sourceArr = source.split("");
// iterate through all the items of sourceArr and targetArr arrays till loop hits the end of shortest array
for (var i = 0; i < Math.min(targetArr.length, sourceArr.length); i++){
// find out the casing of every letter from sourceArr using regular expression
// if sourceArr[i] is upper case then convert targetArr[i] to upper case
if (/[A-Z]/.test(sourceArr[i])) {
targetArr[i] = targetArr[i].toUpperCase();
}
// if sourceArr[i] is not upper case then convert targetArr[i] to lower case
else targetArr[i] = targetArr[i].toLowerCase();
}
// join modified targetArr to string and return
return (targetArr.join(""));
}

// replace "before" with "after" with "before"-casing
return str.replace(before, applyCasing(before, after));
}

// test here
myReplace("A quick brown fox jumped over the lazy dog", "jumped", "leaped");
``````

### Code Explanation:

• Both the before and after are passed as arguments to `applyCasing()`.
• The function `applyCasing()` is used to change the case of respective characters in targetArr i.e., after in accordance with that of characters in sourceArr i.e., before.
• `replace()` is used to replace before with after, whose casing is same as before.

## NOTES FOR CONTRIBUTIONS:

• DO NOT add solutions that are similar to any existing solutions. If you think it is similar but better, then try to merge (or replace) the existing similar solution.
• Categorize the solution in one of the following categories — Basic, Intermediate and Advanced.

See `Wiki Challenge Solution Template` for reference.

Search and Replace: Why is the advanced solution better than the other solutions in the guide?
Question about Intermediate Solution for Search and Replace Challenge
#2

#3

#4

## Here’s a simple, straightforward solution: (And thank you, @Rafase282, for all of your hints and help.)

``````function myReplace(str, before, after) {
if (before[0] === before[0].toUpperCase()) {
after = after.replace(after[0], after[0].toUpperCase());
}
return str.replace(before, after);
}
``````

For Array Lovers here is something short and precise =>

``````
function myReplace(str, before, after) {
return str
.split(" ")
.map((x) => (x == before)?
(x[0] == x[0].toUpperCase()) ?
(after[0].toUpperCase() + after.slice(1)) : after.toLowerCase()
: x)
.join(" ");

}
``````

This also takes care if after starts with an upper case character and before is a lowercase string

#5

Here’s a simple, straightforward solution (white space between lines for clarity):

``````function myReplace(str, before, after) {

\\ IF statement checks to see if the first letter of before (before[0]) is equal to upper case
if (before[0] === before[0].toUpperCase()) {

\\ if before[0] IS upper case, then sets after equal to after with the first letter replaced with upper case
after = after.replace(after[0], after[0].toUpperCase());
}
return str.replace(before, after);
}

myReplace("His name is Tom", "Tom", "john");   //  returns "His name is John"
``````

#6

I solved it like this:-

function myReplace(str, before, after) {

``````if (before[0] === before[0].toUpperCase()) {
after = after[0].toUpperCase() + after.slice(1);
}
``````
``````str = str.replace(before, after);
return str;
``````

}

myReplace(“A quick brown fox jumped over the lazy dog”, “jumped”, “leaped”);

Based on the things we have learned it seemed the easiest solution. Granted it only works on the premise that only the first letter of the word will be capitalised, but it passes all the tests set.

#7

Here’s my solution:

``````function myReplace(str, before, after) {
if (str.charCodeAt(str.indexOf(before)) >= 65 && str.charCodeAt(str.indexOf(before)) <= 90) {
return str.replace(before, after.charAt(0).toUpperCase() + after.slice(1));
}
return str.replace(before, after);
}

myReplace("Let us get back to more Coding", "Coding", "algorithms");
``````

Am I the only one who solved this by checking the unicode values? Probably not as eloquent as the solutions above but it works!

#8

Here is my solution with comments to clarify.
`function myReplace(str, before, after) {
if (before[0] === before[0].toUpperCase()){ //checks if the first character of before is capital
after = after.charAt(0).toUpperCase() + after.slice(1); //if the first character of before is capital then the first character of after is made into a capital
}
var newStr = str.replace(before, after); //create a new string where the before word is replaced with the after word
return newStr; //return that new string
}

myReplace(“A quick brown fox Jumped over the lazy dog”, “Jumped”, “leaped”);`

#9

My quick solution:

function myReplace(str, before, after) {
return str.split(before).join(before[0] == before[0].toUpperCase() ? after.charAt(0).toUpperCase() + after.slice(1): after);
}

myReplace(“He is Sleeping on the couch”, “Sleeping”, “sitting”);

Search and Replace - Better Advanced Solution
#10

I used array functions, to come up with this solution that is case-sensitive beyond the first character.

``````function myReplace (str, before, after) {

var boolArr =  before.split("").map(function (bLet) {
return bLet===bLet.toUpperCase() ? true : false;
});

after = after.split("").map(function (aLet) {
return boolArr[after.indexOf(aLet)] ? aLet.toUpperCase() : aLet.toLowerCase();
}).join("");

return str.replace(before,after);
}
``````
1. List item

#11

Great solution. Very efficient!

#12

My solution -

``````function myReplace(str, before, after) {

if (/[A-Z]/.test(before[0])) {
after = after.replace(after[0],after[0].toUpperCase());
}
return str.replace(before,after);
}``````

#14

function myReplace(str, before, after) {

after = after.split(’’);
if(before.charCodeAt(0)>=65 && before.charCodeAt(0)<=90){
var upCase = after[0].toUpperCase();
after.splice(0,1,upCase);

}

return str.replace(before,after.join(’’));

}

#15

I like this one, more efficient than mine (which is below); one note however, yours could return an unexpected uppercase in ‘after’ if ‘before’ has a number in it. Easily remedied though.

Here’s mine:

``````
function myReplace(str, before, after) {
var after1 = "";
for(var i = 0; i < Math.min(before.length, after.length); i++) {
if(isNaN(before.charAt(i)) && before.charAt(i) === before.charAt(i).toUpperCase()) {
after1 += after.charAt(i).toUpperCase();
}
else if(isNaN(before.charAt(i)) && before.charAt(i) === before.charAt(i).toLowerCase()) {
after1 += after.charAt(i).toLowerCase();
}
else {
after1 += after.charAt(i);
}
}
if(after1.length < after.length) {
after1 += after.slice(after1.length - after.length);
}
return str.replace(before, after1);
}

``````

#16

My solution:

``````function myReplace(str, before, after) {
return str.replace(before, () => before[0] == before[0].toUpperCase() ?
after.replace(after[0], after[0].toUpperCase()) : after);
}``````

#17
``````function myReplace(str, before, after) {
//if (before.charCodeAt(0) < 90) {
if (/[A-Z]/.test(before[0])) {
after = after.split('');
after.splice(0, 1, after[0].toUpperCase());
after = after.join('');
}
return str.replace(new RegExp(before, 'g'), after);
}

myReplace("He is Sleeping on the couch", "Sleeping", "sitting");``````

#18

My solution:

``````function myReplace(str, before, after) {

var toReplace = str.substr(str.indexOf(before), before.length).split("");

if (toReplace[0].toUpperCase() == toReplace[0]) {
after = after.split("")[0].toUpperCase() + after.substr(1);
}

return str.replace(before, after);
}
//test
myReplace("A quick brown fox jumped over the lazy dog", "jumped", "leaped");``````

#19

All of these solutions are all well and good and pass the tests, but what if you need to replace more than one instance of a word in str and maintain case? All of these solutions fail in that case. See https://github.com/freeCodeCamp/freeCodeCamp/issues/15260

#20

This is the best I could come up with that matches the specific case of before and replaces all instances:

``````function myReplace(str, before, after) {

if (/^[A-Z]/.test(before)){
after = after.charAt(0).toUpperCase() + after.slice(1);
}

return str.replace(new RegExp(before, 'g'),after);

}``````

#21

My solutions:

function myReplace(str, before, after) {

``````return str.replace(before, function () {
return before.charCodeAt(0)<=90 ? after.charAt(0).toUpperCase()+after.slice(1) : after.charAt(0).toLowerCase()+after.slice(1);
});
``````

}

and other

function myReplace(str, before, after) {

``````return str.replace(before, function () {
var arrAfter=after.split('');
before.charCodeAt(0)<=90 ? arrAfter.splice(0, 1, after[0].toUpperCase()) : arrAfter.splice(0, 1, after[0].toLowerCase());
return arrAfter.join('');
});
``````

}