数位DP

hdu 2089

#include <cstdio>
#include <cstring>

int dp[10][3], bit[10];

int work(int x)
{
	int i, j, len, k, ans, flag, last;
	memset(bit, 0, sizeof(bit));
	flag = last = ans = len = 0;
	k = x;
	while (x)
	{
		bit[++len] = x%10;
		x /= 10;
	}
	for (i = len; i >= 1; i--)
	{
		ans += dp[i-1][2]*bit[i];
		if (flag) ans += dp[i-1][0]*bit[i];
		else
		{
			if (bit[i] > 4) ans += dp[i-1][0];
			if (bit[i] > 6) ans += dp[i-1][1];
			if (last == 6 && bit[i] > 2) ans += dp[i][1];
		}
		if (last == 6 && bit[i] == 2 || bit[i] == 4) flag = 1;
		last = bit[i];
	}
	return k-ans;
}

int main()
{
	int i, a, b;
	memset(dp, 0, sizeof(dp));
	dp[0][0] = 1;
	for (i = 1; i <= 8; i++)
	{
		dp[i][0] = dp[i-1][0]*9 - dp[i-1][1];
		dp[i][1] = dp[i-1][0];
		dp[i][2] = dp[i-1][2]*10 + dp[i-1][1] + dp[i-1][0];
	}
	while (scanf("%d%d", &a, &b) && a && b)
	{
		printf("%d\n", work(b+1)-work(a));
	}

	return 0;
}

hdu 3555

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>

using namespace std;

long long int dp[21][3];
int bit[21];

void Init()
{
    int i, j;

    memset(dp, 0, sizeof(dp));
    dp[0][0] = 1;
    for (i = 1; i < 20; i++)
    {
        dp[i][0] = dp[i-1][0]*10 - dp[i-1][1];
        dp[i][1] = dp[i-1][0];
        dp[i][2] = dp[i-1][2]*10 + dp[i-1][1];
    }
}

int main()
{
    int T, i, len, flag;
    long long int n, ans;

    Init();
    scanf("%d", &T);
    while (T--)
    {
        scanf("%I64d", &n);
        len = 0;
        n++;
        while (n)
        {
            bit[++len] = n%10;
            n /= 10;
        }
        ans = 0;
        bit[len+1] = 0;
        flag = 0;
        for (i = len; i ; i--)
        {
            ans += dp[i-1][2]*bit[i];
            if (flag)
                ans += dp[i-1][0]*bit[i];
            if (flag == 0 && bit[i] > 4)
                ans += dp[i-1][1];
            if (bit[i] == 9 && bit[i+1] == 4)
                flag = 1;
        }
        printf("%I64d\n", ans);
    }
    
    return 0;
}