reverse() is a predefined function in header file algorithm. It is defined as a template in the above-mentioned header file. It reverses the order of the elements in the range [first, last) of any container. The time complexity is O(n).
Note: The range used is [first, last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
Syntax:
void reverse(BidirectionalIterator first, BidirectionalIterator last) BidirectionalIterator is an iterator that can be used to access any elements of a container in both forward and backward direction.
Examples:
Input : 10 11 12 13 14 15 16 17 Output :10 11 12 13 14 17 16 15 Explanation: reverse(v.begin() + 5, v.begin() + 8); In the above function, input we have applied reverse() on the vector from index 5 to index 7. Therefore when we display the vector we get reverse order from index 5 to index 7.
C++
// CPP program to illustrate // std::reverse() function of STL #include <algorithm> #include <iostream> #include <vector> using namespace std;
int main()
{ vector< int > vec1;
vector< int >::iterator p;
// Inserting elements in vector
for ( int i = 0; i < 8; i++) {
vec1.push_back(i + 10);
}
// Displaying elements of vector
cout<< "Initial Vector:" <<endl;
for (p = vec1.begin(); p < vec1.end(); p++) {
cout << *p << " " ;
}
cout << endl;
cout << "Reverse only from index 5 to 7 in vector:\n" ;
// Reversing elements from index 5 to index 7
reverse(vec1.begin() + 5, vec1.begin() + 8);
// Displaying elements of vector after Reversing
for (p = vec1.begin(); p < vec1.end(); p++) {
cout << *p << " " ;
}
cout << endl <<endl;
vector< int > vec2{ 4, 5, 6, 7 };
cout<< "Initial Vector:" <<endl;
for (p = vec2.begin(); p < vec2.end(); p++) {
cout << *p << " " ;
}
cout << endl;
cout << "Reverse full Vector:" <<endl;
// Reversing directly from beginning to end
reverse(vec2.begin(), vec2.end());
// Displaying elements of vector after Reversing
for (p = vec2.begin(); p < vec2.end(); p++) {
cout << *p << " " ;
}
cout << endl;
return 0;
} |
Output
Initial Vector: 10 11 12 13 14 15 16 17 Reverse only from index 5 to 7 in vector: 10 11 12 13 14 17 16 15 Initial Vector: 4 5 6 7 Reverse full Vector: 7 6 5 4
Time complexity: O(n)
Auxiliary Space: O(1)
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