What is the most efficient algorithm to shift array elements at specified indices left and right by one position?
For example shift indices [1,3,5] of [a,b,c,d,e,f] to the left to get [b,a,d,c,f,e]
I don't want it to rotate if the new index is out of bounds, if that makes sense.
I am using C++ std::vector for array storage.
I'm interpreting your question as to swap the two adjacent entries of an array based on index. If this is wrong, then please clarify your question with an example for which this is not correct.
void swapElements(const std::vector<int>& indexes, std::vector<int>& array){
for(auto i : indexes){
if (i < 1 || i >= array.size()){
continue;
}
std::swap(array[i-1], array[i]):
}
}
I think the simplest way is to use std::swap with the element with the given index and the element that preceds it.
For the first element you can use
std::swap( v.front(), v.back() );
Here is an example
#include <iostream>
#include <vector>
#include <algorithm>
int main()
{
std::vector<char> v = { 'a', 'b', 'c', 'd', 'e', 'f' };
for ( char c : v ) std::cout << c << ' ';
std::cout << std::endl;
for ( size_t i : { 1, 3, 5 } )
{
if ( i == 0 ) std::swap( v.front(), v.back() );
else if ( i < v.size() ) std::swap( v[i], v[i-1] );
}
for ( char c : v ) std::cout << c << ' ';
std::cout << std::endl;
return 0;
}
The output is
a b c d e f
b a d c f e
If you do not want to rotate the vector then you can sibstitute the if statement for the following
for ( size_t i : { 1, 3, 5 } )
{
if ( 0 < i && i < v.size() ) std::swap( v[i], v[i-1] );
}
std::swap?