Write a recursive function that reverses the input string
Try this one
string reverse(string &s)
{
if( s.length() == 0 ) // end condtion to stop recursion
return "";
string last(1,s[s.length()-1]); // create string with last character
string reversed = reverse(s.substr(0,s.length()-1));
return last+reversed; // Make he last character first
}
A recursive function must have the following properties
- It must call itself again
- It must have a condition when the recursion ends. Otherwise you have a function which will cause a stack overflow.
This recursive function does basically create a string of the last character and then call itself again with the rest of the string excluding the last character. The real switching happens at the last line where last+reversed is returned. If it would be the other way around nothing would happen.
It is very inefficient but it works to show the concept.
Just to suggest a better way of handling recursion:
String reversal using recursion in C++:
#include <iostream>
#include <string>
using namespace std;
string reverseStringRecursively(string str){
if (str.length() == 1) {
return str;
}else{
return reverseStringRecursively(str.substr(1,str.length())) + str.at(0);
}
}
int main()
{
string str;
cout<<"Enter the string to reverse : ";
cin>>str;
cout<<"The reversed string is : "<<reverseStringRecursively(str);
return 0;
}
I'll instead explain the recursive algorithm itself. Take the example "input" which should produce "tupni". You can reverse the string recursively by
- If the string is empty or a single character, return it unchanged.
- Otherwise,
- Remove the first character.
- Reverse the remaining string.
- Add the first character above to the reversed string.
- Return the new string.