120. Valid Palindrome

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String Inspection

r

a

c

e

c

a

r

Left Pointer

Right Pointer

Meeting Point

Process Step

Initialize left and right pointers at both ends of the string.

Variables

left0

right7

leftCharNone

rightCharNone

statusComparing

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Example 1:

Input: s = "A man, a plan, a canal: Panama"

Output: true

Explanation: After removing non-alphanumeric characters and converting to lowercase, the string becomes "amanaplanacanalpanama", which is a palindrome.

Example 2:

Input: s = "race a car"

Output: false

Explanation: After removing non-alphanumeric characters and converting to lowercase, the string becomes "raceacar", which is not a palindrome.

Example 3:

Input: s = ""

Output: true

Explanation: An empty string is considered a palindrome.

Example 4:

Input: s = "."

Output: true

Explanation: A string with only non-alphanumeric characters is considered a palindrome after processing.

Example 5:

Input: s = "0P"

Output: false

Explanation: After converting to lowercase and removing non-alphanumeric characters, the string becomes "0p", which is not a palindrome.

Constraints:

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Time Complexity

O(n)

Space Complexity

O(1)

120. Valid Palindrome

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120. Valid Palindrome

Understand Before Coding

String Inspection

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Constraints:

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