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C++ Algorithm reverse()C++ Algorithm reverse() function is used to reverse the order of the elements within a range [first, last). Syntaxtemplate <class BidirectionalIterator> void reverse (BidirectionalIterator first, BidirectionalIterator last); Note: BidirectionalIterator is an iterator which is used to access any elements of a container in both forward and backward direction.Parameterfirst: A bidirectional iterator pointing the position of the first element in the range in which the elements are being reversed. last: A forward iterator pointing the position one past the final element in the range in which the elements are being reversed. Return valueNone ComplexityComplexity is linear in the range [first, last): swaps elements. Data racesThe object in the range [first, last) are modified. ExceptionsThis function throws an exception if either an element is swapped or an operation on iterator throws an exception. Note: The invalid parameters cause an undefined behavior.Example 1Let's see the simple example to reverse the given string: #include <algorithm> #include <iostream> #include <string> using namespace std; int main() { string str = "Hello Myself Nikita"; cout << "Before Reverse : "<< str << endl; reverse(str.begin(), str.end()); cout <<"After Reverse : " << str << endl; return 0; } Output: Before Reverse : Hello Myself Nikita After Reverse : atikiN flesyM olleH Example 2Let's see another simple example to reverse the range of numbers: #include <vector> #include <algorithm> #include <iostream> using namespace std; int main( ) { vector <int> v1; vector <int>::iterator Iter1; int i; for ( i = 0 ; i <= 9 ; i++ ) { v1.push_back( i ); } cout << "The original vector v1 is:\n ( " ; for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ ) cout << *Iter1 << " "; cout << ")." << endl; // Reverse the elements in the vector reverse (v1.begin( ), v1.end( ) ); cout << "The modified vector v1 with values reversed is:\n ( " ; for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ ) cout << *Iter1 << " "; cout << ")." << endl; return 0; } Output: The original vector v1 is: ( 0 1 2 3 4 5 6 7 8 9 ). The modified vector v1 with values reversed is: ( 9 8 7 6 5 4 3 2 1 0 ). Example 3Let's see another simple example: #include<iostream> #include<algorithm> #include<vector> using namespace std; int main() { vector <int> v ; // Inserting elements in vector for (int i = 0; i < 8; i++) v.push_back(i+10); // Displaying elements of vector vector <int> :: iterator it; cout<<"Before: "; for (it = v.begin(); it != v.end(); it++) cout << (*it) << " "; cout << "\n\nReverse only from index 5 to 7 in array:\n"; // Reversing elements from index 5 to index 7 reverse(v.begin() + 5, v.begin() + 8); for (it = v.begin(); it != v.end(); it++) cout << (*it) << " "; // Reversing directly from beginning to end cout << "\nReverse full array:\n"; int a[] = {4, 5, 6, 7}; reverse(begin(a), end(a)); // Print the array cout << a[0] << a[1] << a[2] << a[3] << '\n'; return 0; } Output: Before: 10 11 12 13 14 15 16 17 Reverse only from index 5 to 7 in array: 10 11 12 13 14 17 16 15 Reverse full array: 7654 Example 4Let's see another simple example: #include <iostream> #include <algorithm> #include <vector> #include <iomanip> using namespace std; void print(string a[], int N) { for(int i = 0; i < N; i++) { cout << (i + 1) << ". " << setw(5) << a[i] << " "; } cout << endl; } int main() { string s[] = {"George", "John", "Nik", "Alice", "Bob", "Watson"}; cout << "Original order : "; print(s, 6); cout << "\nReversing the order ... " << endl; reverse(s, s + 6); cout << "Reversed order : "; print(s, 6); } Output: Original order : 1. George 2. John 3. Nik 4. Alice 5. Bob 6. Watson Reversing the order .... Reversed order : 1. Watson 2. Bob 3. Alice 4. Nik 5. John 6. George
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