Write a Program to left shift of an array by one position?

Answer 1

Arrays cannot be left-shifted. That term applies to bit values (it is a bitwise operator). Although conceptually the same, when we shift an array's elements we must traverse the array from the first to penultimate element, copying the next element in place of the current element as we go. This is usually referred to as shunting, and can be done in either direction (left and right).

It's actually much easier think of a left shunt by one element as simply meaning delete the first element. But in reality what you actually do is shunt all the elements (except the first) one position to the left and delete the last element since it will then be a copy of the penultimate element. Alternatively, after shunting all the elements to the left, you can replace the final element with a default value (akin to filling the last bit with a zero as per a bitwise left shift).

The following example demonstrates both techniques using a C++ vector (which is exactly the same as a dynamic array in C but is considerably easier to implement):

#include <iostream>

#include <vector>

// Type definitions to simplify the code.

typedef std::vector<int> int_array;

typedef int_array::iterator it;

void shift_left(int_array& a)

{

// Shift all elements to the left by one position

// and delete the final element.

if( a.size() )

{

unsigned int idx=0;

for(it i=a.begin()+1; i!=a.end(); ++i)

{

a[idx]=a[idx+1];

++idx;

}

a.pop_back();

a.shrink_to_fit();

}

}

void shift_left(int_array& a, int default_value)

{

// Shift all elements to the left by one position

// and replace the final element with the given

// default value.

if( a.size() )

{

unsigned int idx=0;

for(it i=a.begin()+1; i!=a.end(); ++i)

{

a[idx]=a[idx+1];

++idx;

}

a[idx]=default_value;

}

}

void print_array(int_array& a)

{

using namespace std;

for(it i=a.begin(); i!=a.end(); ++i )

cout<<" "<<*i;

cout<<endl;

}

int main()

{

int_array a;

for(int i=0; i<9; ++i )

a.push_back( i+1 );

print_array( a );

shift_left( a );

print_array( a );

shift_left( a, 0 );

print_array( a );

return(0);

}

Output:

1 2 3 4 5 6 7 8 9

2 3 4 5 6 7 8 9

3 4 5 6 7 8 9 0