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'.

Code:

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

解题思路

• 用首尾指针法，遍历字符串；
• 遇到首尾指针所指元素不相同的情况，使用helper函数判断(start+1, end)或者(start, end-1)的情况是否为palindrome；
• helper函数同样使用首尾指针法判断字符串是否为palindrome。