> For the complete documentation index, see [llms.txt](https://algorithm.prettylog.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://algorithm.prettylog.com/algorithm-problems/algoexpert/medium/longest-palindromic-substring.md).

# Longest Palindromic Substring

![](/files/d9wPFqWy3dBGNEGFPGog)

* n^2, n

```tsx
function longestPalindromicSubstring(str) {

  let longest = [0, 1];
  
  for (let i = 0; i < str.length - 1; i++) {
    
    const odd = getLongestPalindrome(str, i, i);
    const even = getLongestPalindrome(str, i, i + 1);
    const current = odd[1] - odd[0] > even[1] - even[0] ? odd : even;
    longest = current[1] - current[0] > longest[1] - longest[0] ? current : longest;
  }

  return str.slice(longest[0], longest[1]);
  
}

function getLongestPalindrome(str, s, e) {

  while (s >= 0 && e < str.length) {
    if (str[s] !== str[e]) break;
    s--;
    e++;
  }

  return [s + 1, e];
}

function isPalidrome(str, s, e) {
  
  while (s <= e) {
    if (str[s] !== str[e]) 
      return false;
    s++;
    e--;
  }

  return true;
}

// Do not edit the line below.
exports.longestPalindromicSubstring = longestPalindromicSubstring;
```