Reddit DailyProgrammer Solution 2017-11-13

solution.js

//  Prompt: https://www.reddit.com/r/dailyprogrammer/comments/7cnqtw/20171113_challenge_340_easy_first_recurring/

//  Solution 1:
//  This solution is 0-indexed.
//  In the worst case scenario, this creates and checks a number
//  of substrings equal to the length of inputStr. Not very efficient.

function firstRecurring(inputStr) {
  var charArr = inputStr.split('');
  for (var i = 0; i < charArr.length; i++) {
    var mySubStr = inputStr.slice(i + 1, inputStr.length);
    if (mySubStr.includes(charArr[i])) {
      console.log("Duplicate char '" + charArr[i] + "' found at index " + (mySubStr.indexOf(charArr[i]) + i + 1));
      return;
    }
  }
  console.log("No duplicate characters found.");
}

//  Solution 2: Inspired by pkoepke's solution.
//  This solution is 0-indexed.
//  O(n) time, where n is the length of inputStr.

function newFirstRecurring(inputStr) {
  var charArr = inputStr.split('');
  var isCharPresent = {}; // empty object
  for (var i = 0; i < charArr.length; i++) {
    if (isCharPresent[charArr[i]] === undefined) {
      isCharPresent[charArr[i]] = true;
    }
    else {
      var mySubStr = inputStr.slice(i + 1, inputStr.length); // Slicing off the first occurrence of the char...
      console.log("Duplicate char '" + charArr[i] + "' found at index " + (mySubStr.indexOf(charArr[i]) + i + 1)); //...So that we can call indexOf
      return;
    }
  }
  console.log("No duplicate characters found.");
}