freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-javascript/69bc6cb30c1d112a2e110a06.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
69bc6cb30c1d112a2e110a06	Challenge 249: String Math	28	challenge-249

--description--

Given a string with numbers and other characters, perform math on the numbers based on the count of non-digit characters between the numbers.

• If the count of characters separating two numbers is even, use addition.
• If it's odd, use subtraction.
• Consecutive digits form a single number.
• Operations are applied left to right.
• Ignore leading and trailing characters that aren't digits.

For example, given "3ab10c8", return 5. Add 3 and 10 to get 13 because there's an even number of characters between them. Then subtract 8 from 13 because there's an odd number of characters between the result and 8.

--hints--

doMath("3ab10c8") should return 5.

assert.equal(doMath("3ab10c8"), 5);

doMath("6MINUS4") should return 2.

assert.equal(doMath("6MINUS4"), 2);

doMath("9plus3") should return 12.

assert.equal(doMath("9plus3"), 12);

doMath("5fkwo#10i#%.<>15P=@20!#B/25") should return 15.

assert.equal(doMath("5fkwo#10i#%.<>15P=@20!#B/25"), 15);

doMath("a.67,1$lk6ldf34@#LD@]2d32d2'2l3,@l3L#@2gh35s09if=df#$t9sm49t0df3$^%[vc;:0:4mt") should return 67.

assert.equal(doMath("a.67,1$lk6ldf34@#LD@]2d32d2'2l3,@l3L#@2gh35s09if=df#$t9sm49t0df3$^%[vc;:0:4mt"), 67);

--seed--

--seed-contents--

function doMath(str) {

  return str;
}

--solutions--

function doMath(str) {
  const tokens = str.match(/(\d+)|(\D+)/g);
  let result = null;
  let pendingOp = null;

  for (const token of tokens) {
    if (/^\d+$/.test(token)) {
      if (result === null) {
        result = parseInt(token);
      } else {
        result = pendingOp === 'add' ? result + parseInt(token) : result - parseInt(token);
      }
    } else {
      pendingOp = token.length % 2 === 0 ? 'add' : 'subtract';
    }
  }

  return result;
}