#include<bits/stdc++.h>

#define LL long long

#define LD long double

#define ull unsigned long long

#define fi first

#define se second

#define mk make_pair

#define PLL pair<LL, LL>

#define PLI pair<LL, int>

#define PII pair<int, int>

#define SZ(x) ((int)x.size())

#define ALL(x) (x).begin(), (x).end()

using namespace std;

const int N = 4e5 + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 + ;

const double eps = 1e-;

const double PI = acos(-);

template<class T, class S> inline void add(T& a, S b) {a += b; if(a >= mod) a -= mod;}

template<class T, class S> inline void sub(T& a, S b) {a -= b; if(a < ) a += mod;}

template<class T, class S> inline bool chkmax(T& a, S b) {return a < b ? a = b, true : false;}

template<class T, class S> inline bool chkmin(T& a, S b) {return a > b ? a = b, true : false;}

int n, m, a[N];

vector<PII> seg;

vector<int> vc;

vector<int> ans;

ull HashVal;

ull hs[N], Pow[N];

ull getHash(int L, int R) {

    return hs[R] - hs[L - ] * Pow[R - L + ];

}

int main() {

    for(int i = Pow[] = ; i < N; i++) Pow[i] = Pow[i - ] * ;

    scanf("%d%d", &n, &m);

    if(n ==  || n == m) return puts(""), ;

    for(int i = ; i <= n; i++) scanf("%d", &a[i]);

    sort(a + , a +  + n);

    a[n + ] = m;

    a[] = -;

    for(int i = ; i <= n; i++)

        if(a[i] +  < a[i + ])

            seg.push_back(mk(a[i] + , a[i + ] - ));

    seg.push_back(mk(-, -));

    seg.push_back(mk(m, m));

    sort(ALL(seg));

    for(int i = ; i < SZ(seg) - ; i++)

        for(int j = seg[i].se + ; j < seg[i + ].fi; j++)

            vc.push_back((j + a[]) % m), vc.push_back((j + a[]) % m - m);

    sort(ALL(vc));

    for(int i = n - ; i >= ; i--) HashVal *= , HashVal += a[i + ] - a[i];

    n--;

    for(int i = ; i < SZ(vc); i++) hs[i] = hs[i - ] *  + vc[i] - vc[i - ];

    for(int i = SZ(vc) / ; i < SZ(vc); i++)

        if(getHash(i - n + , i) == HashVal) ans.push_back(vc[i]);

    printf("%d\n", SZ(ans));

    for(auto& t : ans) printf("%d ", t);

    if(SZ(ans))puts("");

    return ;

}

/*

*/