HDU 3555 Bomb (数位dp)

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <algorithm>
#define MOD 1000000007
#define INF 0x7fffffff
using namespace std;
typedef long long ll;
int bit[70];
ll f[70][5];

ll dp(int pos, int sta, int flag)
{
//第len到pos+1位的数字已确定，现在要确定第pos位
//sta=0则前面确定的序列不含49，sta=1则第pos-1位为4，sta=2则前面确定的序列包含49
//flag=1，不论该位为多少都比N小
if(pos == 0) return sta == 2;
if(flag && f[pos][sta] != -1) return f[pos][sta];
int x = flag ? 9 : bit[pos];
ll ans = 0;
for(int i = 0; i <= x; i++)
{
if(sta == 2 || (sta == 1 && i == 9))
{
ans += dp(pos - 1, 2, flag || i < x);
}
else if(i == 4)
{
ans += dp(pos - 1, 1, flag || i < x);
}
else
{
ans += dp(pos - 1, 0, flag || i < x);
}
}
if(flag) f[pos][sta] = ans;
return ans;
}

ll cal(ll n)
{
int len = 0;
while(n)
{
bit[++len] = n % 10;
n /= 10;
}
ll ans = dp(len, 0, 0);
return ans;
}

int main()
{
#ifdef LOCAL
freopen("dpdata.txt", "r", stdin);
#endif

int t;
ll n;
scanf("%d", &t);
memset(f, -1, sizeof(f));
while(t--)
{
scanf("%I64d\n", &n);
printf("%I64d\n", cal(n));
}

return 0;
}