389. Find the Difference LeetCode

Question

I was solving this problem on Leetcode but I am unable to understand why my solution is wrong I am using the hash map approach to solve this, the time complexity is O(n) but the error is not something related to time exceeding

Question:

You are given two strings s and t.

String t is generated by random shuffling string s and then add one more letter at a random position.

Return the letter that was added to t.

Example 1:

Input: s = "abcd", t = "abcde"
Output: "e"
Explanation: 'e' is the letter that was added.
Example 2:

Input: s = "", t = "y"
Output: "y"
 

Constraints:

0 <= s.length <= 1000

my Solution

var findTheDifference = function (s, t) {

    let mapSet = {}
    let final = ""

    s.split('').forEach((elem) => {

        mapSet[elem] === undefined ? mapSet[elem] = 1 : mapSet[elem]++
    })

    t.split('').forEach((elem) => {

        mapSet[elem] === undefined ? mapSet[elem] = 1 : mapSet[elem]--


        if (mapSet[elem] != 0) {
           
            final = elem
        }
    })

    return final
};

the Error was for this testcase ->

s =
"ymbgaraibkfmvocpizdydugvalagaivdbfsfbepeyccqfepzvtpyxtbadkhmwmoswrcxnargtlswqemafandgkmydtimuzvjwxvlfwlhvkrgcsithaqlcvrihrwqkpjdhgfgreqoxzfvhjzojhghfwbvpfzectwwhexthbsndovxejsntmjihchaotbgcysfdaojkjldprwyrnischrgmtvjcorypvopfmegizfkvudubnejzfqffvgdoxohuinkyygbdzmshvyqyhsozwvlhevfepdvafgkqpkmcsikfyxczcovrmwqxxbnhfzcjjcpgzjjfateajnnvlbwhyppdleahgaypxidkpwmfqwqyofwdqgxhjaxvyrzupfwesmxbjszolgwqvfiozofncbohduqgiswuiyddmwlwubetyaummenkdfptjczxemryuotrrymrfdxtrebpbjtpnuhsbnovhectpjhfhahbqrfbyxggobsweefcwxpqsspyssrmdhuelkkvyjxswjwofngpwfxvknkjviiavorwyfzlnktmfwxkvwkrwdcxjfzikdyswsuxegmhtnxjraqrdchaauazfhtklxsksbhwgjphgbasfnlwqwukprgvihntsyymdrfovaszjywuqygpvjtvlsvvqbvzsmgweiayhlubnbsitvfxawhfmfiatxvqrcwjshvovxknnxnyyfexqycrlyksderlqarqhkxyaqwlwoqcribumrqjtelhwdvaiysgjlvksrfvjlcaiwrirtkkxbwgicyhvakxgdjwnwmubkiazdjkfmotglclqndqjxethoutvjchjbkoasnnfbgrnycucfpeovruguzumgmgddqwjgdvaujhyqsqtoexmnfuluaqbxoofvotvfoiexbnprrxptchmlctzgqtkivsilwgwgvpidpvasurraqfkcmxhdapjrlrnkbklwkrvoaziznlpor"

t =
"qhxepbshlrhoecdaodgpousbzfcqjxulatciapuftffahhlmxbufgjuxstfjvljybfxnenlacmjqoymvamphpxnolwijwcecgwbcjhgdybfffwoygikvoecdggplfohemfypxfsvdrseyhmvkoovxhdvoavsqqbrsqrkqhbtmgwaurgisloqjixfwfvwtszcxwktkwesaxsmhsvlitegrlzkvfqoiiwxbzskzoewbkxtphapavbyvhzvgrrfriddnsrftfowhdanvhjvurhljmpxvpddxmzfgwwpkjrfgqptrmumoemhfpojnxzwlrxkcafvbhlwrapubhveattfifsmiounhqusvhywnxhwrgamgnesxmzliyzisqrwvkiyderyotxhwspqrrkeczjysfujvovsfcfouykcqyjoobfdgnlswfzjmyucaxuaslzwfnetekymrwbvponiaojdqnbmboldvvitamntwnyaeppjaohwkrisrlrgwcjqqgxeqerjrbapfzurcwxhcwzugcgnirkkrxdthtbmdqgvqxilllrsbwjhwqszrjtzyetwubdrlyakzxcveufvhqugyawvkivwonvmrgnchkzdysngqdibhkyboyftxcvvjoggecjsajbuqkjjxfvynrjsnvtfvgpgveycxidhhfauvjovmnbqgoxsafknluyimkczykwdgvqwlvvgdmufxdypwnajkncoynqticfetcdafvtqszuwfmrdggifokwmkgzuxnhncmnsstffqpqbplypapctctfhqpihavligbrutxmmygiyaklqtakdidvnvrjfteazeqmbgklrgrorudayokxptswwkcircwuhcavhdparjfkjypkyxhbgwxbkvpvrtzjaetahmxevmkhdfyidhrdeejapfbafwmdqjqszwnwzgclitdhlnkaiyldwkwwzvhyorgbysyjbxsspnjdewjxbhpsvj"




Output
"j"

Expected
"t"

Answer 1

Your solution failed for console.log(findTheDifference("ab", "cab")). The correct way would be to start with the longer string, t. Then use your algorithm, and finally return the letter of the value that is 1.

var findTheDifference = function(s, t) {

  let mapSet = {}
  let final = ""

  t.split('').forEach((elem) => {
    mapSet[elem] = (mapSet[elem] || 0) + 1
  })

  s.split('').forEach((elem) => {
    mapSet[elem]--
  })

  var result = Object.keys(mapSet).find((elem) => mapSet[elem])
  return result
};

// used to fail for:
console.log(findTheDifference("ab", "cab"))

// test #2: 
s =
"ymbgaraibkfmvocpizdydugvalagaivdbfsfbepeyccqfepzvtpyxtbadkhmwmoswrcxnargtlswqemafandgkmydtimuzvjwxvlfwlhvkrgcsithaqlcvrihrwqkpjdhgfgreqoxzfvhjzojhghfwbvpfzectwwhexthbsndovxejsntmjihchaotbgcysfdaojkjldprwyrnischrgmtvjcorypvopfmegizfkvudubnejzfqffvgdoxohuinkyygbdzmshvyqyhsozwvlhevfepdvafgkqpkmcsikfyxczcovrmwqxxbnhfzcjjcpgzjjfateajnnvlbwhyppdleahgaypxidkpwmfqwqyofwdqgxhjaxvyrzupfwesmxbjszolgwqvfiozofncbohduqgiswuiyddmwlwubetyaummenkdfptjczxemryuotrrymrfdxtrebpbjtpnuhsbnovhectpjhfhahbqrfbyxggobsweefcwxpqsspyssrmdhuelkkvyjxswjwofngpwfxvknkjviiavorwyfzlnktmfwxkvwkrwdcxjfzikdyswsuxegmhtnxjraqrdchaauazfhtklxsksbhwgjphgbasfnlwqwukprgvihntsyymdrfovaszjywuqygpvjtvlsvvqbvzsmgweiayhlubnbsitvfxawhfmfiatxvqrcwjshvovxknnxnyyfexqycrlyksderlqarqhkxyaqwlwoqcribumrqjtelhwdvaiysgjlvksrfvjlcaiwrirtkkxbwgicyhvakxgdjwnwmubkiazdjkfmotglclqndqjxethoutvjchjbkoasnnfbgrnycucfpeovruguzumgmgddqwjgdvaujhyqsqtoexmnfuluaqbxoofvotvfoiexbnprrxptchmlctzgqtkivsilwgwgvpidpvasurraqfkcmxhdapjrlrnkbklwkrvoaziznlpor"

t =
"qhxepbshlrhoecdaodgpousbzfcqjxulatciapuftffahhlmxbufgjuxstfjvljybfxnenlacmjqoymvamphpxnolwijwcecgwbcjhgdybfffwoygikvoecdggplfohemfypxfsvdrseyhmvkoovxhdvoavsqqbrsqrkqhbtmgwaurgisloqjixfwfvwtszcxwktkwesaxsmhsvlitegrlzkvfqoiiwxbzskzoewbkxtphapavbyvhzvgrrfriddnsrftfowhdanvhjvurhljmpxvpddxmzfgwwpkjrfgqptrmumoemhfpojnxzwlrxkcafvbhlwrapubhveattfifsmiounhqusvhywnxhwrgamgnesxmzliyzisqrwvkiyderyotxhwspqrrkeczjysfujvovsfcfouykcqyjoobfdgnlswfzjmyucaxuaslzwfnetekymrwbvponiaojdqnbmboldvvitamntwnyaeppjaohwkrisrlrgwcjqqgxeqerjrbapfzurcwxhcwzugcgnirkkrxdthtbmdqgvqxilllrsbwjhwqszrjtzyetwubdrlyakzxcveufvhqugyawvkivwonvmrgnchkzdysngqdibhkyboyftxcvvjoggecjsajbuqkjjxfvynrjsnvtfvgpgveycxidhhfauvjovmnbqgoxsafknluyimkczykwdgvqwlvvgdmufxdypwnajkncoynqticfetcdafvtqszuwfmrdggifokwmkgzuxnhncmnsstffqpqbplypapctctfhqpihavligbrutxmmygiyaklqtakdidvnvrjfteazeqmbgklrgrorudayokxptswwkcircwuhcavhdparjfkjypkyxhbgwxbkvpvrtzjaetahmxevmkhdfyidhrdeejapfbafwmdqjqszwnwzgclitdhlnkaiyldwkwwzvhyorgbysyjbxsspnjdewjxbhpsvj"

console.log(findTheDifference(s, t))