backspace-string-compare.js

/**

Given two strings s and t, return true if they are equal when both are typed into empty text editors. '#' means a backspace character.

Note that after backspacing an empty text, the text will continue empty.

 

Example 1:

Input: s = "ab#c", t = "ad#c"
Output: true
Explanation: Both s and t become "ac".
Example 2:

Input: s = "ab##", t = "c#d#"
Output: true
Explanation: Both s and t become "".
Example 3:

Input: s = "a#c", t = "b"
Output: false
Explanation: s becomes "c" while t becomes "b".


 */

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var backspaceCompare = function (s, t) {
  let i = s.length - 1;
  let j = t.length - 1;

  let skipS = 0;
  let skipT = 0;

  while (i >= 0 || j >= 0) {
    while (i >= 0) {
      if (s[i] === "#") {
        skipS++;
        i--;
      } else if (skipS > 0) {
        skipS--;
        i--;
      } else {
        break;
      }
    }

    while (j >= 0) {
      if (t[j] === "#") {
        skipT++;
        j--;
      } else if (skipT > 0) {
        skipT--;
        j--;
      } else {
        break;
      }
    }

    let firstChar = i < 0 ? "$" : s[i];
    let secondChar = j < 0 ? "$" : t[j];

    if (firstChar !== secondChar) {
      return false;
    }

    i--;
    j--;
  }

  return true;
};