HDU 3709 Balanced Number

标签（空格分隔）： 数位DP

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题目链接

枚举作为枢纽的点,注意零的情况

#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 T,num[20];
ll f[20][20][10000];
ll dp(int step,int pos,int r,int lim)
{
	if(step==0)return r==0;
	if(!lim&&~f[step][pos][r])return f[step][pos][r];
	int x=lim?num[step]:9;ll res=0;
	for(int i=0;i<=x;i++)
	{
		if(step==pos){res+=dp(step-1,pos,r,lim&&i==x);continue;}
		if(r+(step-pos)*i<0)continue;
		res+=dp(step-1,pos,r+(step-pos)*i,lim&&i==x);
	}
	if(!lim)f[step][pos][r]=res;
	return res;
}
ll calc(ll x)
{
	if(x<0)return 0;
	if(x==0)return 1;
	int len=0;
	while(x)num[++len]=x%10,x/=10;
	ll res=1-len;
	for(int i=1;i<=len;i++)res+=dp(len,i,0,1);
	return res;
}
int main()
{
	memset(f,-1,sizeof(f));
	int T=read();
	while(T--)
	{
		ll L=read(),R=read();
		printf("%lld\n",calc(R)-calc(L-1));
	}
	return 0;
}