Write a Program to Reverse a String

There are a number of ways one can reverse strings. Here are a few of them. These should be enough to impress the interviewer! The methods span from recursive to non-recursive (iterative).

Also note that there is a similar question about reversing the words in a sentence, but still keeping the words in place. That is


I am a good boy


would become


boy good a am I


This is dealt with in another question. Here I only concentrate on reversing strings. That is


I am a good boy


would become


yob doog a ma I



Here are some sample C programs to do the same


Method1 (Recursive)


#include

static char str[]="STRING TO REVERSE";

int main(int argc, char *argv)
{
printf("\nOriginal string : [%s]", str);

// Call the recursion function
reverse(0);

printf("\nReversed string : [%s]", str);
return(0);
}

int reverse(int pos)
{
// Here I am calculating strlen(str) everytime.
// This can be avoided by doing this computation
// earlier and storing it somewhere for later use.

if(pos<(strlen(str)/2)) { char ch; // Swap str[pos] and str[strlen(str)-pos-1] ch = str[pos]; str[pos]=str[strlen(str)-pos-1]; str[strlen(str)-pos-1]=ch; // Now recurse! reverse(pos+1); } } Method2 #include #include #include void ReverseStr ( char *buff, int start, int end )
{
char tmp ;

if ( start >= end )
{
printf ( "\n%s\n", buff );
return;
}

tmp = *(buff + start);
*(buff + start) = *(buff + end);
*(buff + end) = tmp ;

ReverseStr (buff, ++start, --end );
}


int main()
{
char buffer[]="This is Test";
ReverseStr(buffer,0,strlen(buffer)-1);
return 0;
}




Method3


public static String reverse(String s)
{
int N = s.length();
if (N <= 1) return s; String left = s.substring(0, N/2); String right = s.substring(N/2, N);
return reverse(right) + reverse(left);
}





Method4

for(int i = 0, j = reversed.Length - 1; i < j; i++, j--)
{
char temp = reversed[i];
reversed[i] = reversed[j];
reversed[j] = temp;
}
return new String(reversed);





Method5


public static String reverse(String s)
{
int N = s.length();
String reverse = "";
for (int i = 0; i < N; i++)
reverse = s.charAt(i) + reverse;
return reverse;
}





Method6

public static String reverse(String s)
{
int N = s.length();
char[] a = new char[N];
for (int i = 0; i < N; i++)
a[i] = s.charAt(N-i-1);
String reverse = new String(a);
return reverse;
}