Solution to 20/12/19 Devmat problem

uber.ts

const countTokens = (tokenMatcher: RegExp, input: string) =>
  input
    .match(tokenMatcher)
    ?.map((token: string) =>
      token.replace(/((\+|\-|^){1}$(?![0-9]))/g, match => (match === '-' ? '-1' : '1')),
    )
    .map(token => parseInt(token))
    .reduce((accumulator, currentValue) => accumulator + currentValue, 0) ?? 0;

const countVariables = (input: string) => countTokens(/((\+|\-|^)|(-*)[0-9]){1}(?=x)/g, input);
const countConstants = (input: string) => countTokens(/(-|\+|^){1}[0-9](?!x)/g, input);

function solve(input: string): string {
  const [left, right] = input.split('=');
  const totalX = countVariables(left) - countVariables(right);
  const totalConstants = countConstants(left) - countConstants(right);

  if (totalX !== 0) return `x=${-totalConstants / totalX}`;
  if (totalConstants === 0) return 'Infinite solutions';
  return 'No solution';
}