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c++stringstack
Balkrishna Harode
Balkrishna Harode

Reputation: 1

How can I assign stack values to string in C++ without reversing the string?

I want to assign the values in stack to the string without using the method used below. Are there any possible ways/method to perform this in C++? *Assuming there are character values present in the stack.

stack<char> K;
string ans="";
while(!K.empty()){
ans+=K.top();
K.pop();
}
reverse(ans.begin(),ans.end());
return ans;

Thank you in advance.

Upvotes: 0

Views: 2106

Answers (2)

a.koptan
a.koptan

Reputation: 1248

One way of doing it in linear time without reversing at the end:

string str;
str.resize(K.size());
size_t back = str.size() - 1;

while(!K.empty()){
    str[back--] = K.top();
    k.pop();
}

Upvotes: 1

Andrey Semashev
Andrey Semashev

Reputation: 10604

With C++11 and later, you could do something like this:

stack<char> K;
string ans;
ans.resize(K.size());
auto it = ans.rbegin(); // use reverse iteration over the string
while (!K.empty()) {
    *it = K.top();
    K.pop();
    ++it;
}

A more efficient solution would be to not use the stack in the first place. Or, at least, you could use your own stack class that allows to export its contents in forward order:

class my_char_stack :
    public std::stack<char>
{
public:
    void export_string(std::string& str)
    {
        // std::stack has protected member c, which is the container with
        // its elements stored in forward order
        str.append(c.begin(), c.end());
    }
};

my_char_stack K;
string ans;
K.export_string(ans);

Upvotes: 1

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