title: How to parse a string to an integer without library functions?
body: <p>I was recently asked this question in an interview:</p>
  
  <p>"How could you parse a string of the form '12345' into its integer representation 12345 without using any library functions, and regardless of language?"</p>
  
  <p>I thought of two answers, but the interviewer said there was a third.  Here are my two solutions:</p>
  
  <p>Solution 1: Keep a dictionary which maps '1' => 1, '2' => 2, etc.  Then parse the string one character at a time, look up the character in your dictionary, and multiply by place value.  Sum the results.</p>
  
  <p>Solution 2: Parse the string one character at a time and subtract '0' from each character.  This will give you '1' - '0' = 0x1, '2' - '0' = 0x2, etc.  Again, multiply by place value and sum the results.</p>
  
  <p>Can anyone think of what a third solution might be?</p>
  
  <p>Thanks.</p>