1.2 Write code to reverse a C-Style String. (C-String means that "abcd" is represented as five characters, including the null character.)
This one is quite easy:
# -*- coding:utf-8 -*-
import string
# There is no NULL at the end of a string in Python,
# so we use blank space '' as indicator of end
def reverseCStyleStr(str):
length = len(str) - 1
# One cannot change a string,
# so we copy it as a sequence
strSeq = [i for i in str]
for i in range(0, (length+1)//2):
strSeq[i], strSeq[length-1-i] = strSeq[length-1-i], strSeq[i]
return string.join(strSeq)
if __name__ == '__main__':
#str = '12345 '
str = '1234 '
print reverseCStyleStr(str)
Note that the first line of above code gives the program the ability to deal with wide characters.
As the standard answer says, the only "gotcha" is to try to do it in place and be careful for the null character.
One thing to mention is that, I was so stupid that I came up with a "big improvement": split the string evenly, then swap the two segments. Although this solution runs in O(1), it is totally wrong because it doesn't reverse the string...
I even tried to implement it as:
#include <cstring>
#include <cstdio>
void reverseCStyleStr(char* pStr)
{
int nStrLen = strlen(pStr);
// Calculate the head of right part
int nOffset = 0;
if (nStrLen%2 == 0)
{
nOffset = nStrLen/2;
}
else
{
nOffset = nStrLen/2 + 1;
}
char* pRightHead = pStr + nOffset;
// Memory for swaping
char* pTmp = new char[nStrLen/2];
// Swap left part and right part
memcpy(pTmp, pStr, nStrLen/2);
memcpy(pStr, pRightHead, nStrLen/2);
memcpy(pRightHead, pTmp, nStrLen/2);
delete[] pTmp;
}
int main()
{
char* pStr = new char[6];
memcpy(pStr, "12345", 6);
// DO NOT USE: char* pStr = "12345";
reverseCStyleStr(pStr);
printf("%s", pStr);
getchar();
delete[] pStr;
return 0;
}
Although it's a wrong solution, it taught me something about literal strings. Note that the commented line in main function is wrong. You can never change a literal string, because it's in the const pool. Thus, when I firstly used this line, I got a exception about illegal memory access when I wanted to swap the two parts of a string.