C++ String Exercises: Reverse the words of three or more lengths in a string

Last update on November 12 2022 16:01:40 (UTC/GMT +8 hours)

C++ String: Exercise-32 with Solution

Write a C++ program that takes a string and reverses the words of three or more lengths in a string. Return the new string. As input characters, only spaces and letters are permitted.

Sample Data:
("The quick brown fox jumps over the lazy dog") -> “ehT kciuq nworb xof spmuj revo eht yzal god”
("Reverse the words of three or more") -> “esreveR eht sdrow of eerht or erom”
("ABcDef") -> “feDcBA”

Sample Solution:

C++ Code:

#include <bits/stdc++.h>

using namespace std;

std::string test(std::string text) {
	int i = 0;
	int l = text.size();
	while (i < l) {
		size_t j = text.find(' ', i);
		if (j == text.npos) j = l;
		if (i + 3 <= j) std::reverse(&text[i], &text[j]);
		i = j + 1;
	}
	return text;
}

int main() {
  string text = "The quick brown fox jumps over the lazy dog";
  //string text ="ABcDef";
  //string text = "Reverse the words of three or more";
  cout << "Original string: " << text;
  cout << "\n\nReverse the words of three or more lengths of the said string:\n";
  cout << test(text) << endl;
}

Sample Output:

Original string: The quick brown fox jumps over the lazy dog

Reverse the words of three or more lengths of the said string:
ehT kciuq nworb xof spmuj revo eht yzal god

Flowchart:

C++ Code Editor:

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Previous C++ Exercise: Check whether a string is uppercase or lowercase.

Next C++ Exercise: Check first string contains letters from the second.

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C++ Programming: Tips of the Day

What is the usefulness of `enable_shared_from_this?

It enables you to get a valid shared_ptr instance to this, when all you have is this. Without it, you would have no way of getting a shared_ptr to this, unless you already had one as a member.

class Y: public enable_shared_from_this
{
public:

    shared_ptr f()
    {
        return shared_from_this();
    }
}

int main()
{
    shared_ptr p(new Y);
    shared_ptr q = p->f();
    assert(p == q);
    assert(!(p < q || q < p)); // p and q must share ownership
}

The method f() returns a valid shared_ptr, even though it had no member instance. Note that you cannot simply do this:

class Y: public enable_shared_from_this
{
public:

    shared_ptr f()
    {
        return shared_ptr(this);
    }
}

The shared pointer that this returned will have a different reference count from the "proper" one, and one of them will end up losing and holding a dangling reference when the object is deleted.

Ref : https://bit.ly/3pwVzzz