LeetCode 125. Valid Palindrome

 1 #include <iostream>
 2 #include <string>
 3 #include <cctype>  // toupper, isalnum
 4 #include <algorithm>  // transform
 5 using namespace std;
 6 
 7 class Solution {
 8 public:
 9     bool isPalindrome(string s) 
10     {
11          string sTemp = "", sReverse = "";
12 
13          // Convert characters to UPPER
14          transform(s.begin(), s.end(), s.begin(), ::toupper);
15 
16          // considering only alphanumeric characters
17          for (int i = 0; i < s.length(); i ++)
18              if (isalnum(s.at(i)))
19                 sTemp.push_back(s.at(i)); // Appends character to the end of the string, increasing its length by one.
20 
21          // Need to allocate space if use reverse_copy
22          sReverse.resize(sTemp.length());
23          reverse_copy(sTemp.begin(), sTemp.end(), sReverse.begin());
24 /*
25          sReverse = sTemp;
26          reverse(sReverse.begin(), sReverse.end());
27 */         
28 /*
29          cout << sTemp << endl;
30          cout << sReverse << endl;
31 */         
32          return sTemp == sReverse;
33     }
34     
35     bool isPalindrome2(string s) 
36     {
37          int start = 0, end = s.length() - 1;
38 
39          while (start < end)
40          {
41                if ( !isalnum(s.at(start)) ) 
42                   start ++;
43                else if ( !isalnum(s.at(end)) ) 
44                     end --;
45                else if (toupper(s.at(start)) != toupper(s.at(end))) // Remember toupper 
46                       return false;
47                else
48                {
49                    // Remember to move ptr
50                    start ++;
51                    end --;
52                }
53          }
54          
55          return true;
56     }
57     
58 };
59 
60 int main ()
61 {
62     Solution testSolution;
63     string sTest[] = {"A man, a plan, a canal: Panama", "race a car"};
64     
65     for (int i = 0; i < 2; i ++)
66         cout << testSolution.isPalindrome(sTest[i]) << endl;
67     
68     getchar();
69     
70     return 0;
71 }