Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của ladpro98

program c11pines;
uses    math;
const   fi='';
        maxN=12345;
var     a:array[1..maxN] of longint;
        n,d:longint;
        res:int64;

procedure input;
var     inp:text;
        i:longint;
begin
        assign(inp,fi);
        reset(inp);
        readln(inp,n,d);
        for i:=1 to n do
        read(inp,a[i]);
        close(inp);

end;

procedure swap(i,j:longint);
var     t:longint;
begin
        t:=a[i];
        a[i]:=a[j];
        a[j]:=t;
end;

procedure sort(l,r:longint);
var     i,j,p:longint;
begin
        if l>=r then exit;
        p:=a[random(r-l+1)+l];
        i:=l;j:=r;
        repeat
                while a[i]<p do inc(i);
                while a[j]>p do dec(j);
                if i<=j then
                begin
                        if i<j then swap(i,j);
                        inc(i);dec(j);
                end;
        until i>j;
        sort(l,j);sort(i,r);
end;

procedure process;
var     i,modul:longint;
begin
        modul:=a[1] mod d;
        for i:=2 to n do
        if a[i] mod d<>modul then
        begin
                res:=-1;
                exit;
        end;
        res:=0;
        for i:=2 to n do
        res:=res+(a[i]-a[1]) div d;

end;

begin
        input;
        sort(1,n);
        process;
        write(res);
end.

Code mẫu của hieult

#include <set>
#include <map>
#include <list>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <iomanip>
#include <iostream>
#include <algorithm>
#include <fstream>
#include <ctime>
#include <deque>
#include <bitset>
#include <cctype>
#include <utility>
#include <cassert>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef unsigned int ui;
typedef unsigned long long ull;

#define Rep(i,n) for(int i = 0; i < (n); ++i)
#define Repd(i,n) for(int i = (n)-1; i >= 0; --i)
#define For(i,a,b) for(int i = (a); i <= (b); ++i)
#define Ford(i,a,b) for(int i = (a); i >= (b); --i)
#define Fit(i,v) For(__typeof((v).begin()) i = (v).begin(); i != (v).end(); ++i)
#define Fitd(i,v) For(__typeof((v).rbegin()) i = (v).rbegin(); i != (v).rend(); ++i)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define sz(a) ((int)(a).size())
#define all(a) (a).begin(), (a).end()
#define ms(a,x) memset(a, x, sizeof(a))

template<class F, class T> T convert(F a, int p = -1) { stringstream ss; if (p >= 0) ss << fixed << setprecision(p); ss << a; T r; ss >> r; return r; }
template<class T> T gcd(T a, T b) { T r; while (b != 0) { r = a % b; a = b; b = r; } return a; }
template<class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
template<class T> T sqr(T x) { return x * x; }
template<class T> T cube(T x) { return x * x * x; }
template<class T> int getbit(T s, int i) { return (s >> i) & 1; }
template<class T> T onbit(T s, int i) { return s | (T(1) << i); }
template<class T> T offbit(T s, int i) { return s & (~(T(1) << i)); }
template<class T> int cntbit(T s) { return __builtin_popcount(s); }
const int bfsz = 1 << 16; char bf[bfsz + 5]; int rsz = 0;int ptr = 0;
char gc() { if (rsz <= 0) { ptr = 0; rsz = (int) fread(bf, 1, bfsz, stdin); if (rsz <= 0) return EOF; } --rsz; return bf[ptr++]; }
void ga(char &c) { c = EOF; while (!isalpha(c)) c = gc(); }
int gs(char s[]) { int l = 0; char c = gc(); while (isspace(c)) c = gc(); while (c != EOF && !isspace(c)) { s[l++] = c; c = gc(); } s[l] = '\0'; return l; }
template<class T> bool gi(T &v) {
    v = 0; char c = gc(); while (c != EOF && c != '-' && !isdigit(c)) c = gc(); if (c == EOF) return false; bool neg = c == '-'; if (neg) c = gc();
    while (isdigit(c)) { v = v * 10 + c - '0'; c = gc(); } if (neg) v = -v; return true;
}

typedef pair<int, int> II;

const ld PI = acos(ld(-1.0));
const ld eps = 1e-9;

const int inf = (int)1e9 + 5;
const ll linf = (ll)1e17 + 5;
int dr[8] = {-1, +1, 0, 0, +1, +1, -1, -1};
int dc[8] = {0, 0, +1, -1, -1, +1, -1, +1};
const ll mod = 1000000007;

#define maxn 500005

int n, d;
ll a[maxn];

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
//    freopen("in.txt", "r", stdin);
    cin >> n >> d;
    For(i, 1, n) cin >> a[i];
    sort(a + 1, a + n + 1);
    bool ok = true;
    ll res = 0;
    For(i, 1, n){
        if((a[i] - a[1]) % d){
            ok = false;
        }
        res += (a[i] - a[1]) / d;
    }
    if(ok) cout << res << endl;
    else cout << -1 << endl;

    return 0;

}