[TS] Parse a string to an integer

Posted 2020-10-09 Answer1215

A common interview question is to write? a?function?that?converts? a? string?into?an?integer e.g. "123" => 123.? This? function ?is commonly? called? atoi because? we? are? converting? an? ASCII? string? into ?an ?integer.

In this lesson we cover the proper way to do this in javascript which is parseInt along with implementing it using basic ascii math.

 

Writing a function whichi convert string to number, to do that

1. Convert each "string" char to ASCII code by using 

str.charCodeAt(index)

2. Each round, we should increase the acc value by *10

 

function atoi (str: string): number {
  const zeroCode = ‘0‘.charCodeAt(0);
  console.log("zeroCode", zeroCode);
  
  let sub = 1;
  if(str[0] === ‘-‘) {
    sub = -1;
    str = str.substring(1);
    console.log("sub string", str);
  }
  
  return sub * str.split(‘‘)
    .reduce((acc, curr) => {
    acc = acc * 10 + (curr.charCodeAt(0) - zeroCode)    
    return acc;
     }, 0)
}

console.log(atoi("123")); //123
console.log(atoi("-123")); //-123

 

import { atoi } from ‘./atoi‘;

test(‘basic‘, () => {
  expect(atoi(‘123‘)).toBe(123);
  expect(atoi(‘-1123‘)).toBe(-1123);
});