Design a dynamic (resizable) array


Problem Statement

Design a Dynamic (resizable) Array class, such as an ArrayList in Java or a vector in C++

Your DynamicArray class should support the following operations:

If we call pushback(int n) but the array is full, we should resize the array first.

Solution

Also refer this GFG article: Implement your own Vector class

class DynamicArray
{
private:
int *arr; // Points to block of heap memory containing array elements
int size; // Number of filled elements
int capacity; // Total elements the current array can hold
public:
// Parameterized constructor initialization
DynamicArray(int _capacity) : size(0), capacity(_capacity) {
arr = new int[_capacity];
}
// Get size and capacity of current array
int getSize() { return size; }
int getCapacity() { return capacity; }
// Get/Set element at index 'i' (Assuming index within bounds)
int get(int i) { return arr[i]; }
void set(int i, int n) { arr[i] = n; }
void resize()
{
int *old = arr; // To keep track of existing elements
arr = new int[capacity * 2]; // Set current array as new double-capacity one
for (int i = 0; i < size; i++) {
// Copy elements from existing array into new one
arr[i] = old[i];
}
capacity *= 2; // Capacity doubles (size unchanged)
delete[] old; // De-allocate previous array's memory
}
void pushback(int val)
{
// Fully-filled, no space in current array
if (size == capacity) {
resize();
}
// Last element present at 'size-1' index. Insert after it
arr[size] = val;
size++;
}
int popback()
{
// Mark filled elements as one less from end
if (size > 0) {
size--;
}
return arr[size];
}
};