【BZOJ】4292: [PA2015]Równanie

题解

\(f(n)\)的取值范围最多\(9^2 * 18\)

直接枚举判断就好

代码

#include <bits/stdc++.h>
#define fi first
#define se second
#define pii pair<int,int>
#define pdi pair<db,int>
#define mp make_pair
#define pb push_back
#define enter putchar('\n')
#define space putchar(' ')
#define eps 1e-8
#define mo 974711
#define MAXN 500005
//#define ivorysi
using namespace std;
typedef long long int64;
typedef double db;
template<class T>
void read(T &res) {
    res = 0;char c = getchar();T f = 1;
    while(c < '0' || c > '9') {
	if(c == '-') f = -1;
	c = getchar();
    }
    while(c >= '0' && c <= '9') {
	res = res * 10 + c - '0';
	c = getchar();
    }
    res *= f;
}
template<class T>
void out(T x) {
    if(x < 0) {x = -x;putchar('-');}
    if(x >= 10) {
	out(x / 10);
    }
    putchar('0' + x % 10);
}
int64 k,a,b;
int Calc(int64 t) {
    int res = 0;
    while(t) {
	res += (t % 10) * (t % 10);
	t /= 10;
    }
    return res;
}
void Solve() {
    read(k);read(a);read(b);
    int cnt = 0;
    for(int i = 1 ; i <= 2000 ; ++i) {
	if(b / i < k) break;
	int64 t = k * i;
	if(a <= t && t <= b) {
	    if(Calc(t) == i) cnt++;
	}
    }
    out(cnt);enter;
}
int main() {
#ifdef ivorysi
    freopen("f1.in","r",stdin);
#endif
    Solve();
    return 0;
}