2016 World Final E Forever Young

题意:

。。

思路:

xjb搞一下就行了。

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#pragma comment(linker,"/STACK:102400000,102400000")
using namespace std;


#define eps 1e-10
#define N 200020
#define B 20
#define M 3000020
#define inf 0x3f3f3f3f
#define LL long long
#define pii pair
#define MP make_pair
#define fi first
#define se second
#define mod 1000000007

#define md (ll + rr >> 1)


LL n, l;
LL ans;
int a[N];

void check(LL b) {
    if(b < 10) return;
    LL nn = n;
    int len = 0;
    while(nn) {
        LL t = nn % b;
        if(t > 9) return;
        nn /= b;
        a[len++] = t;
    }
    reverse(a, a + len);
    LL tmp = 0;
    for(int i = 0; i < len; ++i) tmp = tmp * 10 + a[i];
    if(tmp < l) return;
    if(ans == -1 || ans < b) ans = b;
}

void solve(LL a, LL b, LL c, LL &x) {
    LL l = 1, r = sqrt(c + 0.5);
    while(l < r) {
        LL mid = (l + r) / 2;
        if(1.0 * mid * (a * mid + b) > 5e18) r = mid;
        else if(mid * (a * mid + b) < c) l = mid + 1;
        else r = mid;
    }
    if(l * (a * l + b) == c) x = l;
    else x = -1;
}

int main() {
    ans = -1;
    cin >> n >> l;
    for(int x = 1; x <= 9; ++x) {
        for(int y = 0; y <= 9; ++y) {
            if((n - y) % x) continue;
            LL b = (n - y) / x;
            if(b < 10) continue;
            check(b);
        }
    }
    for(int a = 1; a <= 9; ++a) {
        for(int b = 0; b <= 9; ++b) {
            for(int c = 0; c <= 9; ++c) {
                LL x1;
                solve(a, b, n - c, x1);
                check(x1);
            }
        }
    }
    for(int i = 10; 1LL * i * i * i <= n; ++i) check(i);
    cout << ans << endl;
    return 0;
}



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