梦熊 数学题

#include<bits/stdc++.h>
using namespace std;
const int MAXN=200010;
const int mod=1e9+7;
int n,a,sum;
int num[MAXN];
int dp[MAXN][12][2],vis[100];
string l, r;
int read(){
	int x=0;
	int f=1;
	char ch=getchar();
	while(ch<'0' || ch>'9'){
		if(ch=='-'){
			f=-1;
		}
		ch=getchar();
	}
	while(ch>='0' && ch<='9'){
		x=x*10+ch-'0';
		ch=getchar();
	}
	return x*f;
}
int to(int x){
	return 1<<x;
}
int dfs(int pos,int st,int s,int lim,int zero) {
	if(s<0 || s>pos){
		return 0;
	}
	if(dp[pos][s][lim]!=-1){
		return dp[pos][s][lim];
	}
	if(!pos){
		return dp[pos][s][lim]=(s==0);
	}
	int maxx=(lim?num[pos]:9);
	int minn=(zero?1:0);
	int tmp=0;
	for(int i=minn;i<=maxx;i++){
		if((to(i) & st)==0){
			(tmp+=dfs(pos-1,st | to(i),s-1,lim && (i==maxx),0))%=mod;
		}
		else{
			(tmp+=dfs(pos-1,st | to(i),s,lim && (i==maxx),0))%=mod;
		}
	}
	return dp[pos][s][lim]=tmp;
}
int check(string s){
	int sss=a;
	int siz=s.size();
	for(int i=0;i<siz;i++){
		int x=s[i]-'0';
		if(!vis[x]){
			vis[x]=1;
			sss--;
			if(sss<0){
				return 0;
			}
		}
	}
	if(sss==0){
		return 1;
	}
	return 0;
}

int solve(string s) {
	sum = 0;
	int siz = s.size();
	for(int i=siz-1;i>=0;i--){
		num[++sum]=s[i]-'0';
	}
	memset(dp,-1,sizeof(dp));
	return dfs(sum,0,a,1,1);
}
void ppp() {
	int siz=l.size();
	for(int i=0;i<siz;i++){
		if(r[i]>l[i]){
			return;
		}
		else if(r[i]<l[i]){
			printf("0\n");
			exit(0);
		}
	}
	return;
}
signed main() {
	freopen("math.in","r",stdin);
	freopen("math.out","w",stdout);
	n=read();
	cin>>l>>r;
	ppp();
	a=read();
	printf("%d\n",((solve(r)-solve(l)+mod)%mod+check(l))%mod);
	return 0;
}