HDU 3555 - Bomb

第一道数位dp，属于基础模板，又自卑小时没学好数数了，只是不清楚为什么大家的dp定义都是相同的，很显然么，难道我写的是怪胎。。。

/*
ID:esxgx1
LANG:C++
PROG:hdu3555
*/
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;#define LN    21
unsigned long long dp[LN + 1][3];void work(int ln)
{dp[0][0] = 1;for(int i=1; i<=ln; ++i) {dp[i][0] = dp[i-1][0] * 9 + dp[i-1][1] * 8;    // 无49，开头无9dp[i][1] = dp[i-1][0] + dp[i-1][1];            // 无49, 开头是9dp[i][2] = dp[i-1][2] * 10 + dp[i-1][1];    // 有49
//        printf("i=%d, %I64u %I64u %I64u\n", i, dp[i][0], dp[i][1], dp[i][2]);
    }
}unsigned long long solve(int i, unsigned long long N, int &extra)
{unsigned long long prefix = N/10;int curr = N % 10;int extra0 = extra;unsigned long long rslt = N % 10 * dp[i-1][2];if (curr >= 9 && prefix % 10 == 4) extra = 1;if (prefix) rslt += solve(i+1, prefix, extra0);if (extra0) {rslt += curr * (dp[i-1][0] + dp[i-1][1]);extra = 1;} else if (curr > 4) rslt += dp[i-1][1];return rslt;
}int main(void)
{#ifndef ONLINE_JUDGEfreopen("in.txt", "r", stdin);#endifint T;cin >> T;if (T) {work(LN);do {unsigned long long N;cin >> N;int extra = 0;cout << solve(1, N, extra) + (extra ? 1 : 0)<< endl;--T;}while(T);}return 0;
}