[First week][valid-palindrome] adds answer

Author: routiful

valid-palindrome/routiful.py

@@ -0,0 +1,59 @@
+# FIRST WEEK
+
+# Question : 125. Valid Palindrome
+
+# A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and
+# removing all non-alphanumeric characters, it reads the same forward and backward.
+# Alphanumeric characters include letters and numbers.
+# Given a string s, return true if it is a palindrome, or false otherwise.
+
+# Example 1:
+# Input: s = "A man, a plan, a canal: Panama"
+# Output: true
+# Explanation: "amanaplanacanalpanama" is a palindrome.
+
+# Example 2:
+# Input: s = "race a car"
+# Output: false
+# Explanation: "raceacar" is not a palindrome.
+
+# Example 3:
+# Input: s = " "
+# Output: true
+# Explanation: s is an empty string "" after removing non-alphanumeric characters.
+# Since an empty string reads the same forward and backward, it is a palindrome.
+
+# Constraints:
+# 1 <= s.length <= 2 * 105
+# s consists only of printable ASCII characters.
+
+# Notes:
+# Using `reverse`(O(N)) api and matching all(max O(N)) look straightforward.
+# The two pointer method may useful to decrease time complexity.
+# If length of input is 0 or 1, return true.
+
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+        l = len(s)
+        if l < 2:
+            return True
+
+        f = 0
+        b = l - 1
+
+        while (f <= b):
+            if (s[f] == " " or (s[f].isalpha() == False and s[f].isnumeric() == False)):
+                f = f + 1
+                continue
+
+            if (s[b] == " " or (s[b].isalpha() == False and s[b].isnumeric() == False)):
+                b = b - 1
+                continue
+
+            if s[f].lower() != s[b].lower():
+                return False
+
+            f = f + 1
+            b = b - 1
+
+        return True