KINV - Dãy nghịch thế độ dài K
Tác giả: hieult
Ngôn ngữ: C++
#include<cstdio>
#include<cmath>
#include<math.h>
#include<cstring>
#include<cstdlib>
#include<cassert>
#include<ctime>
#include<algorithm>
#include<iterator>
#include<iostream>
#include<cctype>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<list>
#define fi first
#define se second
#define PB push_back
#define MP make_pair
#define ep 0.00001
#define maxn 300011
#define oo 1111111111
#define mod 1000000000
#define TR(c, it) for(typeof((c).begin()) it=(c).begin(); it!=(c).end(); it++)
#define rep(i, n) for(int i = 0; i < int(n); i++)
#define FOR(i, a, b) for(int i = int(a); i <= int(b); i++)
#define FORD(i, a, b) for(int i = int(a); i >= int(b); i--)
//#include <conio.h>
//#define g 9.81
const int bfsz = 1 << 16; char bf[bfsz + 5]; int rsz = 0;int ptr = 0;
char gc() { if (rsz <= 0) { ptr = 0; rsz = 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;
}
double const PI=4*atan(1.0);
using namespace std;
typedef pair<int, int> II;
typedef vector<int> VI;
typedef vector<II> VII;
typedef vector<VI> VVI;
typedef vector<VII> VVII;
void OPEN(){
freopen("A.in","r",stdin);
freopen("A.out","w",stdout);
}
long long f[10010][12] = {0};
int n, k, a[10010];
void update(int x, int i, long long add){
while(x > 0){
f[x][i] = (f[x][i] + add) % mod;
x -= x & -x;
}
}
long long get(int x, int i){
long long ret = 0;
while(x <= 10000){
ret = (ret + f[x][i]) % mod;
x += x & -x;
}
return ret;
}
int main(){
//OPEN();
scanf("%d %d", &n, &k);
FOR(i, 1, n) scanf("%d", &a[i]);
long long res = 0, t;
FOR(j, 1, n){
FOR(i, 1, k){
if(i == 1) t = 1;
else t = get(a[j] + 1, i - 1);
update(a[j], i, t);
if(i == k) res = (res + t) % mod;
}
}
cout << res;
}