[LeetCode][125. Valid Palindrome] Simple Two Pointers Solution

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By Long Luo

This article is the solution Simple Two Pointers Solution of Problem 125. Valid Palindrome.

Very easy, we can use Two Pointers to solve this problem.

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public boolean isPalindrome(String s) {
    if (s == null || s.length() <= 1) {
        return true;
    }

    int n = s.length();
    int left = 0;
    int right = n - 1;
    while (left < right) {
        while (left < n && left < right && !(Character.isDigit(s.charAt(left)) || Character.isAlphabetic(s.charAt(left)))) {
            left++;
        }

        while (right > 0 && left < right && !(Character.isDigit(s.charAt(right)) || Character.isAlphabetic(s.charAt(right)))) {
            right--;
        }

        if (Character.toUpperCase(s.charAt(left)) != Character.toUpperCase(s.charAt(right))) {
            return false;
        }

        while (left < right && Character.toUpperCase(s.charAt(left)) == Character.toUpperCase(s.charAt(right))) {
            left++;
            right--;
        }
    }

    return true;        
}

Analysis

  • Time Complexity: O(n)
  • Space Complexity: O(1)

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