LeetCode : 344. Reverse String

 

这个题目本身来说应该算是学初级入门第一课的难度了，相信学过数组的小朋友就能解决。

比较简单的实现方式有很多，但还是考虑算法的效率问题。

class Solution {
public:
    string reverseString(string s) {
        string temp(s);
        int i=0,len=0;
        len = s.length();
        for(int i=0;i<len;i++){
            temp[i]=s[len-1-i];
        }
        return temp;
    }
};

 

但如果这样，并没有发挥C++语言强大的功能，我们可以试试STL库。

reverse (STL Samples)

template<class BidirectionalIterator> inline
   void reverse(
      BidirectionalIterator First,
      BidirectionalIterator Last
   )

// reverse.cpp
// compile with: /EHsc
// Illustrates how to use the reverse function.
//
// Functions:
//    reverse - Reverse the items in a sequence.

// disable warning C4786: symbol greater than 255 character,
// okay to ignore
#pragma warning(disable: 4786)

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <functional>

using namespace std;


int main()
{
   const int VECTOR_SIZE = 8;

   // Define a template class vector of strings
   typedef vector<string > StrVector;

   //Define an iterator for template class vector of strings
   typedef StrVector::iterator StrVectorIt;

   StrVector Tongue_Twister(VECTOR_SIZE);
   StrVectorIt start, end, it;

   // location of first element of Tongue_Twister
   start = Tongue_Twister.begin();

   // one past the location last element of Tongue_Twister
   end = Tongue_Twister.end();

   //Initialize vector Tongue_Twister
   Tongue_Twister[0] = "she";
   Tongue_Twister[1] = "sells";
   Tongue_Twister[2] = "sea";
   Tongue_Twister[3] = "shells";
   Tongue_Twister[4] = "by";
   Tongue_Twister[5] = "the";
   Tongue_Twister[6] = "sea";
   Tongue_Twister[7] = "shore";

   cout << "Before calling reverse" << endl;

   // print content of Tongue_Twister
   cout << "Try this Tongue Twister:";
   for (it = start; it != end; it++)
      cout << " " << *it;
   cout << endl;

   // reverse the items in the vector Tongue_Twister
   reverse(start, end);

   cout << "After calling reverse" << endl;

   // print content of Tongue_Twister
   cout << "Now try the reversed Tongue Twister:";
   for (it = start; it != end; it++)
      cout << " " << *it;
}

Before calling reverse
Try this Tongue Twister: she sells sea shells by the sea shore
After calling reverse
Now try the reversed Tongue Twister: shore sea the by shells sea sells she

 所以，这道题目可以这样解决：

string reverseString(string s) {
        reverse(s.begin(),s.end());
        return s;
    }

跑476个case，两段代码的时间是相同的，都是12ms，可以推测对于string 的inline而言，实现方式是一样的。