two arrays, find the missing numbers - c++

Question

Given two arrays, first has 'n' numbers and the second one has 'n-m' numbers; the second array is not in the same order as the first. If there are several numbers with the same value, they end up in the order of the positions in the original array. Also, all the values from the second array are also found in the first array. I have to find the 'm' missing numbers in the order in which they appear in the first array.
input:
7 3
12 34 45 29 100 87 32
100 87 12 34
output:
45 29 32
#include <iostream>
using namespace std;
int main()
{
int n, missing_number = 0, m, i, j, v[1201], w[1201];
cin >> n >> m;
for (i = 0; i < n; ++i) {
cin >> v[i];
}
for (i = 0; i < n - m; ++i) {
cin >> w[i];
}
for (i = 0; i < n; ++i) {
missing_number = 1;
for (j = 0; j < n - m; ++j) {
if (v[i] == w[j]) {
missing_number = -1;
}
}
if (missing_number == 1) {
cout << v[i] << " ";
}
}
if (m == 0)
cout << "there are no missing numbers";
return 0;
}
my code doesn't work for repeating numbers like:
7 3
2 6 1 9 3 2 4
4 1 2 3
where my output should be:
6 9 2

Answer 1

Your program seems to be outputting the correct result. However, I felt that I need to refactor your code to improve its readability and remove the bad practices used in it.
The below is the same as your code with a bit of improvement:
#include <iostream>
#include <array>
#include <limits>
int main( )
{
std::array<int, 1201> arr1; // use std::array instead of raw arrays
std::array<int, 1201> arr2;
std::size_t arr1_size { }; // renamed n
std::size_t arr2_size { }; // renamed m
std::cin >> arr1_size >> arr2_size;
if ( arr2_size == 0 ) // this if statement should be here to help end
{ // the program early on to prevent the execution
// of the for-loops
std::cout << "There are no missing numbers.\n";
return 0;
}
for ( std::size_t idx { }; idx < arr1_size; ++idx ) // use std::size_t
{ // for the loop counters
std::cin >> arr1[ idx ];
}
for ( std::size_t idx { }; idx < arr1_size - arr2_size; ++idx )
{
std::cin >> arr2[ idx ];
}
for ( std::size_t arr1_idx { }; arr1_idx < arr1_size; ++arr1_idx )
{
bool isNumberMissing { true }; // this should be of type bool
for ( std::size_t arr2_idx { }; arr2_idx < arr1_size - arr2_size; ++arr2_idx )
{
if ( arr1[ arr1_idx ] == arr2[ arr2_idx ] )
{
isNumberMissing = false;
// this is my trick for solving your code's bug
arr2[ arr2_idx ] = std::numeric_limits<int>::min( );
break; // break here to improve performance
}
}
if ( isNumberMissing )
{
std::cout << arr1[ arr1_idx ] << " ";
}
}
std::cout << '\n';
}
Sample input/output #1:
7 3
12 34 45 29 100 87 32
100 87 12 34
45 29 32
Sample input/output #2:
7 3
2 6 1 9 3 2 4
4 1 2 3
6 9 2
Note: See Why is "using namespace std;" considered bad practice?