125 Valid Palindrome

125. Valid Palindrome​
1. Question
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
For example,
"A man, a plan, a canal: Panama"is a palindrome.
"race a car"isnota palindrome.
Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.
For the purpose of this problem, we define empty string as valid palindrome.
2. Implementation
(1) Two Pointers
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class Solution {
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    public boolean isPalindrome(String s) {
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        if (s == null || s.length() == 0) {
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            return true;
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        }
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​
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        int start = 0, end = s.length() - 1;
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​
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        while (start < end) {
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            if (!Character.isLetterOrDigit(s.charAt(start))) {
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                ++start;
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            }
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            else if (!Character.isLetterOrDigit(s.charAt(end))) {
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                --end;
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            } 
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            else if (Character.toLowerCase(s.charAt(start)) != Character.toLowerCase(s.charAt(end))) {
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                return false;
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            }
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            else {
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                ++start;
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                --end;
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            }
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        }
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        return true;
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    }
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}
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3. Time & Space Complexity
Two Pointers: 时间复杂度O(n), 空间复杂度O(1)

88 Merge Sorted Array

159 Longest Substring with At Most Two Distinct Characters

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Contents

125. Valid Palindrome

1. Question

2. Implementation

3. Time & Space Complexity

125. Valid Palindrome​

1. Question

2. Implementation

3. Time & Space Complexity

125. Valid Palindrome