feat:add Solution.cpp for 0125. Valid Palindrome

Author: Stackingrule

solution/0100-0199/0125.Valid Palindrome/Solution.cpp

@@ -0,0 +1,24 @@
+class Solution {
+public:
+    bool isPalindrome(string s) {
+        int left = 0, right = s.size() - 1;
+        while (left < right) {
+            if (!isAlphaNum(s[left])) ++left;
+            else if (!isAlphaNum(s[right])) --right;
+            else if ((s[left] + 32 - 'a') % 32 != (s[right] + 32 - 'a') % 32) return false;
+            else {
+                ++left;
+                --right;
+            }
+        }
+        return true;
+    }
+
+private:
+    bool isAlphaNum(char &ch) {
+        if (ch >= 'a' && ch <= 'z') return true;
+        if (ch >= 'A' && ch <= 'Z') return true;
+        if (ch >= '0' && ch <= '9') return true;
+        return false;
+    }
+};