leetcode solution 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:

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Input: "aba"
Output: True

Example 2:

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

Note:

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

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class  {
    public boolean validPalindrome(String s) {
        int l = 0;
        int r = s.length()-1;
        while(l < r){
            if(s.charAt(l) != s.charAt(r)){
                return isPalindrome(s, l+1, r) || isPalindrome(s, l, r-1);
            }
            l++;
            r--;
        }
        return true;
    }
    public boolean isPalindrome(String s, int l, int r){
        while(l<r){
            if(s.charAt(l) != s.charAt(r)){
                return false;
            }
            else{
                l++;
                r--;
            }
        }
        return true;
    }
}

• The basic idea is to compare the first ant the last character of string s . if s is a palindrome after remove one single letter. we can know that it can be seen as insert a letter into a palindrome.
• so, we can consitently compare the first and the last letter of s , if they’re not the same, we judge the two substring which is the original string removing one of the ends letter.
  • aabbcaa : we consistently judge abbca -> bbc -> bb -> ba