HDU - 3555 Bomb （数位DP）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

long long dp[30][3], n;
int arr[30];

void init() {
dp[0][0] = 1;
dp[0][1] = dp[0][2] = 0;
for (int i = 1; i < 25; 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][1] + dp[i-1][2]*10;
}
}

long long cal(long long n) {
int len = 0;
while (n) {
arr[++len] = n%10;
n /= 10;
}
arr[len+1] = 0;
int flag = 0;
long long ans = 0;
for (int i = len; i >= 1; i--) {
ans += dp[i-1][2] * arr[i];
if (flag)
ans += dp[i-1][0] * arr[i];
else if (arr[i] > 4)
ans += dp[i-1][1];
if (arr[i+1] == 4 && arr[i] == 9)
flag = 1;
}
if (flag)
ans++;
return ans;
}

int main() {
int t;
scanf("%d", &t);
init();
while (t--) {
cin >> n;
cout << cal(n) << endl;
}
return 0;
}