package q5

// Note: Although it can be done in O(N) with, e.g., Manacher's algorithm, the
// input size is small enough to brute-force.

func expand(s string, l, r int) (int, int) {
	for l > 0 && r < len(s)-1 && s[l-1] == s[r+1] {
		l--
		r++
	}
	return l, r
}

func longestPalindrome(s string) string {
	maxLen, mL, mR := 0, 0, 0

	for c := range len(s) {
		l, r := expand(s, c, c)
		len_ := r - l + 1
		if len_ > maxLen {
			maxLen, mL, mR = len_, l, r
		}
	}

	for c := range len(s) - 1 {
		if s[c] == s[c+1] {
			l, r := expand(s, c, c+1)
			len_ := r - l + 1
			if len_ > maxLen {
				maxLen, mL, mR = len_, l, r
			}
		}
	}
	return s[mL : mR+1]
}

var _ = longestPalindrome