hdu 3652 B-number

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3652

题意：

给出一个数N，求1-N中有多少个数，其中出现了13且能被13整除。

思路：数位DP，记忆化搜索判断是否同时满足两个条件。

#include <bits/stdc++.h>
using namespace std;
int num[15];
int n;
int dp[15][15][2][2];
int dfs(int cur, int last, int state, int mark, int limit)
{
    if(cur < 0) 
    {
        if(mark == 1 && last == 0) return 1;
        else return 0;
    }
    if(!limit && dp[cur][last][state][mark] != -1) return dp[cur][last][state][mark];
        
    int up = limit?num[cur]:9;
    int ret = 0;
    for(int i = 0; i <= up; i++)
    {
        int temp = (last*10+i)%13;
        int nowmark;
        
        if(mark == 1) nowmark = 1;
        else if(mark == 0 && state == 1 && i == 3) nowmark = 1;
        else nowmark = 0;
        
        ret += dfs(cur-1, temp, i == 1, nowmark, limit && i == up); 
    }
    if(!limit) dp[cur][last][state][mark] = ret;
    return ret;
}
int slove(int x)
{
    memset(dp, -1, sizeof(dp));
    int cnt = 0;
    while(x)
    {
        num[cnt++] = x%10; 
        x /= 10;
    }
    return dfs(cnt-1, 0, 0, 0, 1);
}
int main() 
{
  //  freopen("in.txt", "r", stdin);
  //  freopen("out.txt", "w", stdout);
    while(~scanf("%d", &n))
    {
        printf("%d\n", slove(n));
    }
    return 0;
}