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KINV.cpp
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KINV.cpp
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#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> ii;
typedef unsigned long long ull;
#define X first
#define Y second
#define pb push_back
#define mp make_pair
#define ep emplace_back
#define EL printf("\n")
#define sz(A) (int) A.size()
#define FOR(i,l,r) for (int i=l;i<=r;i++)
#define FOD(i,r,l) for (int i=r;i>=l;i--)
#define fillchar(a,x) memset(a, x, sizeof (a))
#define faster ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
const int N = 50000, mod = 1000000000;
int n, k, a[N], vt[N];
ll res, f[20][N], t[N];
ll get(int x) {
ll ans = 0;
while (x <= n) {
ans = (ans + t[x]) % mod;
x += x & (-x);
}
return ans;
}
void update(int x, ll add) {
while (x > 0) {
t[x] = (t[x] + add) % mod;
x -= x & (-x);
}
}
int main() {
// freopen("INP.TXT", "r", stdin);
// freopen("OUT.TXT", "w", stdout);
scanf("%d%d", &n,&k);
for (int i=1; i<=n; i++) {
scanf("%d", &a[i]);
vt[a[i]] = i;
}
for (int i=1; i<=n; i++) f[1][i] = 1;
for (int i=2; i<=k; i++) {
for (int j=1; j<=n; j++) t[j] = 0;
for (int j=1; j<=n; j++) {
f[i][j] = get(a[j]+1);
update(a[j], f[i-1][j]);
}
}
for (int i=1; i<=n; i++)
res = (res + f[k][i]) % mod;
printf("%lld", res);
return 0;
}