Longest Palindromic Substring

func longestPalindrome(s string) string {
    ll := len(s)
    if ll == 0 {
        return ""
    }

    var l, r, pl, pr int
    for r < ll {
        // gobble up dup chars
        for r+1 < ll && s[l] == s[r+1] {
            r++
        }
        // find size of this palindrome
        for l-1 >= 0 && r+1 < ll && s[l-1] == s[r+1] {
            l--
            r++
        }
        if r-l > pr-pl {
            pl, pr = l, r
        }
        // reset to next mid point
        l = (l+r)/2 + 1
        r = l
    }
    return s[pl : pr+1]
}