is-valid-num.js

/*
A valid number can be split up into these components (in order):

- A decimal number or an integer.
- (Optional) An 'e' or 'E', followed by an integer.

=> A decimal number can be split up into these components (in order):

-> (Optional) A sign character (either '+' or '-').
-> One of the following formats:
    - One or more digits, followed by a dot '.'.
    - One or more digits, followed by a dot '.', followed by one or more digits.
    - A dot '.', followed by one or more digits.

=> An integer can be split up into these components (in order):

-> (Optional) A sign character (either '+' or '-').
-> One or more digits.

For example, all the following are valid numbers: 
["2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", 
"3e+7", "+6e-1", "53.5e93", "-123.456e789"], 
while the following are not valid numbers: 
["abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53"].

Given a string s, return true if s is a valid number.

isValidNumber("2") => true
isValidNumber("2ac") => false
*/

function isSignCharacter(char) {
  return char === "+" || char === "-";
}

function isAlphabetCharacter(char) {}

/**
 * @param {string} s
 * @return {boolean}
 */
function isValidNumber(s) {
  // YOUR CODE HERE
  // DON'T FORGET TO RETURN BOOLEAN VALUE
  // 1BAC -> 1bac
  const lowerCaseStr = s.toLowerCase();
  const loopedSigns = [];
  for (let i = 0; i < lowerCaseStr.length; i++) {
    // case start with e
    if (lowerCaseStr[i] == "e" && i == 0) {
      return false;
    }

    // case end with e
    if (lowerCaseStr[i] == "e" && i == lowerCaseStr.length - 1) {
      return false;
    }

    if (lowerCaseStr[i] === "-" || lowerCaseStr[i] === "+") {
      loopedSigns.push(lowerCaseStr[i]);
    }

    if (loopedSigns.length > 1) {
      return false;
    }

    if (i > 0 && loopedSigns.length > 0) {
      // case --, ++, -+, +-
      if (
        isSignCharacter(lowerCaseStr[i]) &&
        isSignCharacter(lowerCaseStr[i - 1])
      ) {
        return false;
      }
    }
  }

  return true;
}

// console.log(
//   "isValidNumber -> true",
//   [
//     "2",
//     "0089",
//     "-0.1",
//     "+3.14",
//     "4.",
//     "-.9",
//     "2e10",
//     "-90E3",
//     "3e+7",
//     "+6e-1",
//     "53.5e93",
//     "-123.456e789",
//   ].map(isValidNumber)
// );

console.log(
  "isValidNumber -> false",
  ["1e", "e3", "--6", "-+3", "abc", "1a", "99e2.5", "95a54e53"].map(
    isValidNumber
  )
);

// start with "e"
// end with "e"
// double signs (--, ++, -+, +-)
// start with a-z
// end with with a-z
// after "e", char is "."
// having any a-z char in the middle