Write a Kotlin Program to reverse string with example

Input:
Hello World

Output:
dlroW olleH

Input:
Hi Ram!

Output:
Reversed: !maR iH

1. Program to Reverse a string

Pseudo Algorithm

• Use a temp variable result that stores reversed string. Initialize it with empty string.
• Iterate given string from end index to start start.
• For each position, get the string at that index and append it in string result
• Terminate the loop when we reach to start index.
• Finally, value present in result variable is reversed string.

Sourcecode –

fun main() {

    println("Enter string:")
    val str = readLine()

    var result: String = ""
    var lastIndex = str!!.lastIndex

    while (lastIndex >= 0) {
        result += str[lastIndex]
        lastIndex--
    }

    println("Reversed: $result")
}

When you run the program, output will be –

Enter string:
Hello Rahul! How are you?
Reversed: ?uoy era woH !luhaR olleH

Explanation:

• Read the value entered by user using readLine() function.
  Then, store this value in variable str
• Then, define a variable, result that stores the reversed string.
• Then, get the last index of the string and store it in variable lastIndex.
  We do this to get position of the last character present in string.
• Then, run a while loop from last index, lastIndex, of the string.
• Append each character present at index lastIndex in variable result.
• Then, decrease the value of lastIndex by 1.
• Repeat the loop till we reach at first character in string.

Let’s take an example,

Assume user entered

string = “hello”

Now,
result = “”
lastIndex = 4

run a loop from 4 till lastIndex becomes 0

• After iteration at lastIndex = 4,
  result = “o”
  lastIndex = 3
• After iteration at lastIndex = 3,
  result = “ol”
  lastIndex = 2
• After iteration at lastIndex = 2,
  result = “oll”
  lastIndex = 1
• After iteration at lastIndex = 1,
  result = “olle”
  lastIndex = 0
• After iteration at lastIndex = 0,
  result = “olleh”
  lastIndex = -1

Value at variable result is reversed of variable str.

Thus, we went through Kotlin Program to Reverse a given string.
Similarly, you can use this kotlin program to reverse a sentence.