#640 - Solve the Equation

Medium • View on LeetCode • View on GitHub

Problem Description

Solve a given equation and return the value of 'x' in the form of a string "x=#value".

The equation contains only '+', '-' operation, the variable 'x' and its coefficient.

You should return "No solution" if there is no solution for the equation, or "Infinite solutions" if there are infinite solutions for the equation.

If there is exactly one solution for the equation, we ensure that the value of 'x' is an integer.

Solution

/**
 * @param {string} equation
 * @return {string}
 */
var solveEquation = function(equation) {
  const [left, right] = equation.split('=');
  const leftSide = parseSide(left);
  const rightSide = parseSide(right);
  const totalX = leftSide.xCount - rightSide.xCount;
  const totalNum = rightSide.numSum - leftSide.numSum;

  if (totalX === 0 && totalNum === 0) return 'Infinite solutions';
  if (totalX === 0) return 'No solution';

  return `x=${totalNum / totalX}`;

  function parseSide(side) {
    let xCount = 0;
    let numSum = 0;
    let currentNum = 0;
    let sign = 1;

    for (let i = 0; i < side.length; i++) {
      const char = side[i];
      if (char === 'x') {
        const v = i === 0 || side[i-1] === '+' || side[i-1] === '-';
        xCount += sign * (currentNum === 0 && (v) ? 1 : currentNum);
        currentNum = 0;
      } else if (char === '+' || char === '-') {
        numSum += sign * currentNum;
        sign = char === '+' ? 1 : -1;
        currentNum = 0;
      } else {
        currentNum = currentNum * 10 + parseInt(char);
      }
    }
    numSum += sign * currentNum;

    return { xCount, numSum };
  }
};