Starter Algorithms — Reverse a String

Question: Write a method that reverses a string. Your method will receive one argument, a string, and be expected to output that string with its letters in reverse order.

Input: "hello"
Output: "olleh"
Input: "apples"
Output: "selppa"

Do not call any type of built-in reverse method!

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Please solve the problem using iteration.

JavaScript

Before you start coding

1. Understand the problem

• given an input word, create an algorithm that will print out the word backwards

2. Write your own Test Cases

Input: "hello"
Output: "olleh"
Input: "apples"
Output: "selppa"

3. Devise a plan to solve the problem, pseudocode

• take into account each letter of the word
• initially assign an empty string;
  let newString = "";
• using a for loop iterate through each letter
• start at the last letter and print out each letter into the empty string

input str = "hello"
input str index = "h - 0, e - 1, l - 2, l - 3, o - 4"
input str length = 5 
let newString = "";
for loop:
var i = str.length-1;   
// str.length - 1 = 4; this means you are starting at the 4th index and the last letter, in this case "o"
i >= 0; 
// will run the condition as long as i is greater than or equal to 0, our initial i is 4, which is greater than and equal to 0
i --;
// decrement by one 
1. i = 4, i >= 0, (is 4 greater than or equal to 0 - yes), i -- 
2. i = 3, i >= 0, (is 3 greater than or equal to 0 - yes), i --
3. i = 2, i >= 0, (is 2 greater than or equal to 0 - yes), i --
4. i = 1, i >= 0, (is 1 greater than or equal to 0 - yes), i --
5. i = 0, i >= 0, (is 0 equal to 0 - yes), i --
inside for loop:
newString = newString + str[i]
1. "" = "" + o
2. o = o + l 
3. ol = ol + l
4. oll = oll + e
5. olle = ollo + h
6. olleh
return newString ----> "olleh"

4. Code

function reverseString(str){
  let newString = "";
  for (var i = str.length-1; i >= 0; i --){
    newString = newString + str[i]
  }
    return newString
}

5. Revise

• once you are done the problem see if you can go back and refactor the code to be more efficient
• in this example, we can shorten the condition inside the for loop to fewer words

function reverseString(str){
  let newString = "";
  for (var i = str.length-1; i >= 0; i --){
    newString += str[i]
}
    return newString
}