Timus 1057 Amount of Degrees

标签（空格分隔）： 数位DP

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題目链接

DP 显然每一位只有选一或选0的情况

#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;
typedef long long ll;
ll read()
{
	ll x=0,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 X,Y,K,B,dit[35],dp[35][25];
int dfs(int step,int c,int lim)
{
	if(step==0)return c==K;
	if(lim==0&&dp[step][c]!=-1)return dp[step][c];
	int res=0;
	if(c<K)if(lim==0||dit[step])res+=dfs(step-1,c+1,lim&&dit[step]==1);
	res+=dfs(step-1,c,lim&&dit[step]==0);
	if(lim==0)dp[step][c]=res;
	return res;
}
int calc(int x)
{
	int len=0;
	while(x)dit[++len]=x%B,x/=B;
	return dfs(len,0,1);
}
int main()
{
	memset(dp,-1,sizeof(dp));
	X=read(),Y=read(),K=read(),B=read();
	if(B==1){printf("%d
",(int)(K>=X&&K<=Y));return 0;}
	printf("%d
",calc(Y)-calc(X-1));
	return 0;
}