{}动态规划}记忆化dp

 先搞个模板

#include<stdio.h>
#include<string.h>
using namespace std;
typedef long long ll;
int a[20];
ll dp[20][2];
ll dfs(int pos,bool six,bool limit)
{
    if(pos==0) return six?1:0;
    int state=six?1:0;
    if(!limit&&dp[pos][state]!=-1) return dp[pos][state];
    int up=limit?a[pos]:9;
    ll ans=0;
    for(int i=0;i<=up;++i)
    {
        ans+=dfs(pos-1,six||i==6,limit&&i==a[pos]);
    }
    if(!limit) dp[pos][state]=ans;
    return ans;
}
ll solve(ll x)
{
    memset(dp, -1, sizeof(dp));
    int pos=0;
    while(x)
    {
        a[++pos]=x%10;
        x/=10;
    }
    return dfs(pos,0,1);
}
int main()
{
    ll le,ri;
    scanf("%lld %lld",&le,&ri);
    printf("%lld\n",solve(ri)-solve(le-1));
    return 0;
}