You are given a string equal halves and reverse it

Question

let n = "jsdfnsgnlewnl";
let l = n.length;
let trgt = Math.floor((l-1)/2);


function firstHalf(anyhting){
  let ans = [];
  for (i = trgt; i>=0; i--){
    ans.push(n[i])
  }
  return ans;
}


function lastHlaf (anyhting){
  let ansx = [];
  for (i=l-1; i>=trgt+1; i--){
    ansx.push(n[i])
  }
  return ansx;
}

let answer = firstHalf(n);
let answerx = lastHlaf(n);
let newAnswer = answer.join("");
let newAnswerx = answerx.join("");
console.log(newAnswer+newAnswerx)

in this code the output should be -> snfdsjglnweln

But it's giving --> gsnfdsjlnweln

Can anyone please explain me.

Thank you for example --> //if ithe input is odd like xyzakig //then the middle value should not be changed please help me to understand the issue

Answer 1

Aaaahhh, with your comment concerning odd number of string-length, I think I understood now your question. Hence I edited my initial answer.

1. Initial string jsdfnsgnlewnl to devide into 2 parts

   We get left half jsdfns and right half nlewnl

2. Then invert each block seperately

   We get snfdsj and lnweln

3. Check if initial string-length is odd

   If so, we define the middle element, here g

4. Then join the 2 strings (or 3 strings if odd)

   We get snfdsjglnwelng

Now we get your requested result: snfdsjglnweln

The following code would give you the expected output:

let n = "jsdfnsgnlewnl";
let l = n.length;
let trgt = Math.floor(l/2); // '(l/2) instead of '((l-1)/2)'

let even = Number.isInteger(l/2); // check if 'l' is an even number

function firstHalf(anyhting){
  let ans = [];                 // index 'i' is zero-based:  
  for (i = trgt-1; i>=0; i--){  // 'trgt-1' instead of 'trgt'
    ans.push(n[i])
  }
  return ans;
}

function lastHalf (anyhting){  // corrected typo: 'lastHalf' instead of 'lastHlaf'
  let ansx = [];
  for (i=l-1; i>l-1-trgt; i--){ // 'i>l-1-trgt' instead of 'i>=trgt-1'
    ansx.push(n[i])
  }
  return ansx;
}

let answerMiddle = "";
if (!even) answerMiddle = n[trgt]; // define the "letter in the middle" if odd


let answer = firstHalf(n);
let answerx = lastHalf(n);
let newAnswer = answer.join("");
let newAnswerx = answerx.join("");

console.log(newAnswer + answerMiddle + newAnswerx)  // add also '+answerMiddle'

I tested for even string-lengths as well - worked. Hope I got it right now.