FZU 2109 Mountain Number ---数位dp

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<iostream>
using namespace std;
#define inf 0x3f3f3f3f

int bit[20],dp[20][20][2];

int dfs(int pos,int pre,int p,int first,int flag)
{
if(pos==-1) return 1;
if(!flag&&dp[pos][pre][p]!=-1)
return dp[pos][pre][p];
int sum=0;
int end=flag?bit[pos]:9;
for(int i=0;i<=end;i++)
{
if(first&&!i)
sum+=dfs(pos-1,9,0,1,0);
else if(p&&i>=pre)
sum+=dfs(pos-1,i,0,0,flag&&(i==end));
else if(!p&&i<=pre)
sum+=dfs(pos-1,i,1,0,flag&&(i==end));
}
if(!flag) dp[pos][pre][p]=sum;
return sum;
}
int calc(int x)
{
int i,j,len=0;
while(x)
{
bit[len++]=x%10;
x/=10;
}
return dfs(len-1,9,0,1,1);
}
int main()
{
int t;
cin>>t;
memset(dp,-1,sizeof(dp));
while(t--)
{
int i,j,k;
int a,b;
cin>>a>>b;
printf("%d\n",calc(b)-calc(a-1));
}
}