LeetCode 125. Valid Palindrome
https://leetcode.com/problems/valid-palindrome/
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"
is not a 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.
- 字符串题。两种解法,一种是直接把string翻转比较,另一种是传统的首尾两个指针移动比较。
- 注意对指针-- end,end不能为size_t类型, 否则一旦被减为-1则会被转变为INT_MAX,程序进入死循环。
- 学习了string相关STL算法和函数,往string里添加char用push_back。
- toupper - C++ Reference
- http://www.cplusplus.com/reference/cctype/toupper/
- isalnum - C++ Reference
- http://www.cplusplus.com/reference/cctype/isalnum/?kw=isalnum
- transform - C++ Reference
- http://www.cplusplus.com/reference/algorithm/transform/?kw=transform
- string::push_back - C++ Reference
- http://www.cplusplus.com/reference/string/string/push_back/
- reverse_copy - C++ Reference
- http://www.cplusplus.com/reference/algorithm/reverse_copy/
- reverse_copy
- https://msdn.microsoft.com/zh-cn/library/c7ty5c36.aspx
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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 }