数位dp模版题（杠杆数/平衡数）

洛谷：p1831杠杆题

#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
long long int num[1004] = {};
long long int dp[20][20][2005] = {}, l, r;
long long int dfs(long long int pos,long long int x,bool flag,bool lim, long long int num1)
{
    if(!pos) return num1 == 0;
    if(!lim && dp[pos][x][num1] != -1) return dp[pos][x][num1];
    long long int maxx = lim ? num[pos] : 9, ans = 0;
    for(int i = 0;i <= maxx;i++)
    {
        if(flag) ans += dfs(pos-1,x,flag && i == 0,lim && i == maxx,i*(pos - x));
        else
        {
            ans += dfs(pos-1,x,flag && i == 0,lim && i == maxx,num1 + i*(pos - x));
        }
    }
    if(!lim) dp[pos][x][num1] = ans;
    return ans;
}
long long int solve(long long int x)
{
    long long int ans = 0, cnt = 0;
    while(x) num[++cnt] = x % 10, x/= 10;
    for(int i = 1;i <= cnt;i++)
    {
        ans += dfs(cnt,i,1,1,0);    
    }
    return ans-cnt+1;
}
int main()
{
    memset(dp,-1,sizeof(dp));
    scanf("%lld%lld", &l, &r);
    if(!l) printf("%lld\n", solve(r));
    else printf("%lld\n", solve(r) - solve(l-1));
    return 0;    
}