680. Valid Palindrome II

class Solution {
public:
    bool validPalindrome(string s) {
        int i = 0, j = s.length() - 1;
        while (i < j) {
            if (s[i] == s[j]) {
                i++;
                j--;
            }
            else {
                return helper(s, i+1, j) || helper(s, i, j-1);
            }
        }
        return true;
    }
    bool helper(const string &s, int i, int j) {
        while (i < j) {
            if (s[i] != s[j])   return false;
            i++;
            j--;
        }
        return true;
    }
};