まん中から広げて最も長い回文の部分文字列を探す

def longest_palindrome(
    s
):
    start = 0
    size = 1
    for c in range(len(s)):
        for d in (0, 1):
            lo, hi = grow(
                s, c, c + d
            )
            if hi - lo > size:
                start = lo
                size = hi - lo
    return s[start:start + size]


def grow(s, lo, hi):
    n = len(s)
    while 0 <= lo and hi < n:
        if s[lo] != s[hi]:
            break
        lo -= 1
        hi += 1
    return lo + 1, hi

function longestPalindrome(
  s
) {
  let start = 0;
  let size = 1;
  const n = s.length;
  for (let c = 0; c < n; c++) {
    for (const d of [0, 1]) {
      const [lo, hi] = grow(
        s, c, c + d
      );
      if (hi - lo > size) {
        start = lo;
        size = hi - lo;
      }
    }
  }
  return s.slice(
    start, start + size
  );
}

function grow(s, lo, hi) {
  const n = s.length;
  while (lo >= 0 && hi < n) {
    if (s[lo] !== s[hi]) {
      break;
    }
    lo--;
    hi++;
  }
  return [lo + 1, hi];
}

func longestPalindrome(
	s string,
) string {
	start, size := 0, 1
	for c := 0; c < len(s); c++ {
		for d := 0; d <= 1; d++ {
			lo, hi := grow(s, c, c+d)
			if hi-lo > size {
				start, size = lo, hi-lo
			}
		}
	}
	return s[start : start+size]
}

func grow(
	s string, lo, hi int,
) (int, int) {
	for lo >= 0 && hi < len(s) {
		if s[lo] != s[hi] {
			break
		}
		lo--
		hi++
	}
	return lo + 1, hi
}