传送门
题目描述
在一个长度为 n n n的区间内选 m m m个数,要求这 m m m个数的最大值和最小值的差大于等于 k k k,问有多少种组合情况
分析
数据范围不大,我们可以记录一下每一个数字出现的次数,然后从小到大开始枚举,枚举到的数字必选,然后在从区间范围内选若干个数字即可
这道题卡 m e m s e t memset memset是真的狗
代码
#pragma GCC optimize(3)
#include <bits/stdc++.h>
#define debug(x) cout<<#x<<":"<<x<<endl;
#define dl(x) printf("%lld\n",x);
#define di(x) printf("%d\n",x);
#define _CRT_SECURE_NO_WARNINGS
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> PII;
typedef vector<int> VI;
const int INF = 0x3f3f3f3f;
const int N = 3e5 + 10;
const ll mod= 1000000007;
const double eps = 1e-9;
const double PI = acos(-1);
template<typename T>inline void read(T &a){
char c=getchar();T x=0,f=1;while(!isdigit(c)){
if(c=='-')f=-1;c=getchar();}
while(isdigit(c)){
x=(x<<1)+(x<<3)+c-'0';c=getchar();}a=f*x;}
int gcd(int a,int b){
return (b>0)?gcd(b,a%b):a;}
ll ksm (ll a , ll b){
ll ans = 1 , base = a;
while (b){
if (b & 1) ans = ans * base % mod;b >>= 1;base = base * base % mod;}return ans;}
int n,k;
ll m;
ll cnt[N];
ll a[N];
ll f[N],inv[N];
ll C (ll a,ll b){
if (a < b) return 0;
return f[a] * inv[a - b] % mod * inv[b] % mod;
}
int main(){
int T;
read(T);
f[0] = inv[0] = 1;
for (int i = 1 ; i < N ; i++){
f[i] = f[i - 1] * i % mod;
inv[i] = ksm(f[i] , mod - 2);
}
while(T--){
read(n),read(m),read(k);
for(int i = 1;i <= n + m + 10;i++) cnt[i] = 0;
for(int i = 1;i <= n;i++){
int x;
read(x);
cnt[x]++;
}
for(int i = 1;i <= n;i++) cnt[i] += cnt[i - 1];
ll res = 0;
for(int i = 1;i <= n;i++){
ll sum = cnt[i - 1] - cnt[max(0,i - k - 1)];
ll p = cnt[i] - cnt[i - 1];
for(ll j = 1;j <= min(p,m);j++){
res = (res + C(sum ,m - j) * C(p,j) % mod) % mod;
}
}
dl(res);
}
}
/**
* ┏┓ ┏┓+ +
* ┏┛┻━━━┛┻┓ + +
* ┃ ┃
* ┃ ━ ┃ ++ + + +
* ████━████+
* ◥██◤ ◥██◤ +
* ┃ ┻ ┃
* ┃ ┃ + +
* ┗━┓ ┏━┛
* ┃ ┃ + + + +Code is far away from
* ┃ ┃ + bug with the animal protecting
* ┃ ┗━━━┓ 神兽保佑,代码无bug
* ┃ ┣┓
* ┃ ┏┛
* ┗┓┓┏━┳┓┏┛ + + + +
* ┃┫┫ ┃┫┫
* ┗┻┛ ┗┻┛+ + + +
*/