680. Valid Palindrome II

Given a non-empty string s, you may delete at most one character. Judge whether you can make it a palindrome.

Example 1:

Input: "aba"
Output: True

Example 2:

Input: "abca"
Output: True
Explanation: You could delete the character 'c'.

分析：
先用两个指针: i, j 分别指向字符串的两端，然后一个往前移，一个往后移动。如果遇到不一样，则要么跳过i,要么跳过j，再不断比较。

class Solution {
    public boolean validPalindrome(String s) {
        return validPalindrome(s, 0, s.length() - 1, false);
    }
    
    private boolean validPalindrome(String s, int start, int end, boolean mustMatch) {
        while (start < end) {
            if (s.charAt(start) != s.charAt(end)) {
                if (mustMatch) return false;
                return validPalindrome(s, start + 1, end, true) || validPalindrome(s, start, end - 1, true);
            }
            start++;
            end--;
        }
        return true;
    }
}