codeforce - Soldier and Badges

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define fastread()(ios_base::sync_with_stdio(false),cin.tie(NULL));
int main()
{
    int n;
    scanf("%d",&n);
    int ara[n+1];
    for(int i=0;i<n;i++)scanf("%d",&ara[i]);
    sort(ara,ara+n);
    int c=0;
    for(int i=1;i<n;i++)
    {
        if(ara[i]==ara[i-1])
        {
            c++;
            ara[i]++;
        }
        else if(ara[i]<ara[i-1])
        {
            int a=ara[i-1]-ara[i];
            ara[i]+=a+1;
            c+=a+1;
        }
    }
    printf("%d\n",c);
    return 0;
}