Valid Palindrome II

题目
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'.

Note:
The string will only contain lowercase characters a-z. The maximum length of the string is 50000.

答案

思路是,设2个指针，left和right，一个指向s的头部，一个指向s的尾部，两个指针逐渐向对方靠拢，靠拢的同时判断s[left]是否不等于s[right], 如果不等于的话，检测is_palindrome(s without s[left]) or is_palindrome(s without s[right]), 如果其一是true，则有可能通过删除一个字符达成palindrome

class Solution {
    public boolean isPal(String s, int omit) {
        int left = 0, right = s.length() - 1;
        while(left <= right) {
            if(left == omit) {
                left++;
                continue;
            }
            if(right == omit) {
                right--;
                continue;
            }
            if(s.charAt(left) != s.charAt(right)) return false;
            left++;
            right--;
        }
        return true;
    }
    public boolean validPalindrome(String s) {
        int left = 0, right = s.length() - 1;

        // Base cases
        if(s.length() <= 1) return true;

        while(left <= right) {
            char c1 = s.charAt(left);
            char c2 = s.charAt(right);
            if(c1 != c2) {
                // Is s a palindrome with s[left] or s[right] removed ?
                return isPal(s, left) || isPal(s, right);
            }
            left++;
            right--;
        }
        return true;
    }
}