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0680 - Valid Palindrome II (Easy)

https://leetcode.com/problems/valid-palindrome-ii

Problem Statement​

Given a string s, return true if the s can be palindrome after deleting at most one character from it.

Example 1:

Input: s = "aba"
Output: true

Example 2:

Input: s = "abca"
Output: true
Explanation: You could delete the character 'c'.

Example 3:

Input: s = "abc"
Output: false

Constraints:

  • 1 <= s.length <= 10^5
  • s consists of lowercase English letters.

Approach 1: Brute Force​

To check if a string is a palindrome, we can use two pointers to compare the character at pointer ii and that at pointer jj. If they are not same, then it means it is not a palindrome. However, this problem allows us to delete at most one character from it. Therefore, we do the same way. If there is a difference, that means we can potentially delete the one at pointer ii or the one at pointer jj. We try both case to see if it is possible to form a palindrome.

Written by @wingkwong
class Solution {
public:
    // check palindrome with target range
    bool palindromeWithRange(string s, int i, int j) {
        while (i < j) {
            if (s[i] != s[j]) return false;
            i++, j--;
        }
        return true;
    }
    
    bool validPalindrome(string s) {
        int n = s.size(), i = 0, j = n - 1;
        while (i < j) {
            // not same -> potentially delete s[i] or s[j]
            if (s[i] != s[j]) {
                // try both case
                return palindromeWithRange(s, i, j - 1) || palindromeWithRange(s, i + 1, j);
            }
            i++, j--;
        }
        return true;
    }
};