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Write code to implement pop_front operation for a vector in C++. The pop_front operation should remove the first element from the vector and maintain the order of remaining elements.
Pushing The Rope
We know that std::vector only supports push_back and pop_back operations. Both operations runs in constant time. The pop_front operation will take at-least O(n) time since the vector is backed by an array and all the remaining elements needs to be shifted by one position to the left to preserve the order. If number of pop_front operation is more, std::list container should be preferred which is implemented as double-ended queue (deque).
So pop_front operation will take linear time and should called only if the vector contains only small number of elements. Here’s one feasible implementation of the pop_front function which simply erases the first element of the vector using vector::erase method. The vector::erase function requires an iterator pointing to the element to be removed from the vector and we can get an iterator to the first element of a vector by calling vector::begin.
2 4 6 8 10 12 14 16 18 20 | #include <vector> template<typenameT> { v.erase(v.begin()); } intmain() std::vector<int>nums={1,2,3,4,5}; std::cout<<i<<' '; return0; |
Output:
2 3 4 5
Luckily if we don’t need to maintain the order of the remaining elements in the vector, we have a constant time solution which includes moving the last element of the vector to the front. This can be done with the help of std::move function.
2 4 6 8 10 12 14 16 18 20 22 | #include <vector> template<typenameT> { v.front()=std::move(v.back()); } { pop_front(nums); for(inti:nums) } |
Output:
5 2 3 4
(4 votes, average: 5.00 out of 5)
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JavaScript gives us four methods to add or remove items from the beginning or end of arrays:
pop(): Remove an item from the end of an array
pop() returns the removed item.
push(): Add items to the end of an array
push() returns the new array length.
shift(): Remove an item from the beginning of an array
shift() returns the removed item.
unshift(): Add items to the beginning of an array
unshift() returns the new array length.