HDU 3555

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9
        dp[i][1] = dp[i-1][0] + dp[i-1][1];            // 无49, 开头是9
        dp[i][2] = dp[i-1][2] * 10 + dp[i-1][1];    // 有49
//        printf("i=%d, %I64u %I64u %I64u
", 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_JUDGE
    freopen("in.txt", "r", stdin);
    #endif
    int 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;
}

2014-07-31 20:55:00

Accepted

3555

156MS

348K

1257 B

G++