Highest Value Palindrome

function maximumPalinUsingKChanges(str, k) { let palin = str.split(""); let ans = ""; let l = 0; let r = str.length - 1; let changedArray = []; while (l < r) { if (str[l] != str[r]) { palin[l] = palin[r] = Math.max(str[l], str[r]); changedArray[l] = true; k--; } l++; r--; } if (k < 0) { return "Not possible"; } l = 0; r = str.length - 1; while (l <= r) { if (palin[l] !== 9) { if (changedArray[l] && k > 0) { palin[l] = palin[r] = "9"; k--; } else if (!changedArray[l] && k >= 2) { palin[l] = palin[r] = "9"; k = k - 2; } } if ((l === r) & (k > 0)) { palin[l] = "9"; } l++; r--; } for (let i = 0; i < palin.length; i++) ans += palin[i]; return ans; } let str = "3493"; console.log(str.length); let k = 1; console.log(maximumPalinUsingKChanges(str, k));