Monday, 28 September 2020

Write your own Integer to String (itoa) implementation in Java

Write your own Integer to String (itoa) converter.

Implement your own Integer to ASCII (itoa) method which converts an Integer to String.

Input 1: 123
Output: "123" (as String)

Input 2: 0
Output: "0" (as String)

Input 3: 8
Output: "8" (as String)

Algorithm

Before we look into the algorithm, lets understand the ASCII ranges for 0-9.

ASCII  Char 
--------------- 
 48   0    
 49   1    
 50   2    
 51   3    
 52   4    
 53   5    
 54   6    
 55   7    
 56   8    
 57   9 

so if we have integer 4 and we want to get the char representation of 4, we can get by
char number = '0' + 4 which would be 48 + 4 = 52 and when we do ((char) 52) we get '4'.

similarly, if we have integer 7 and we want to get the char representation of 7, we can get by
char number = '0' + 7 which would be 48 + 7 = 55 and when we do ((char) 55) we get '7'.

Lets jump to original problem, if given the number 123

Mod and Divide the number by 10 to read each digits from end, once we have the digit convert it in the way shown below and put in StringBuilder.

Java Program to convert Integer To Ascii.

package javabypatel;

public class IntegerToASCII {
    public static void main(String[] args) {
        System.out.println(integerToAscii(10));
    }

    private static String integerToAscii(int num) {
        StringBuilder sb = new StringBuilder();
        while (num > 0) {
            int lastDigit = num % 10;
            char ch = (char) ('0' + lastDigit);

            // since we are processing the last digit first(reverse order),
            // inserting at 0th position so that output is not in reverse order.
            sb.insert(0, ch);
            num /= 10;
        }
        return sb.toString();
    }
}
at

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