uva 1549 - Lattice Point(暴力)

uva 1549 - Lattice Point(暴力)

題目鏈接：uva 1549 - Lattice Point

題目大意：給定圓半徑，以原點為圓心，求園內有多少個整數點。

解題思路：首先坐標軸將圓分成4份，所以只要單獨考慮每一塊的個數乘4再加1即可（原點）

#include 
#include 
#include 
#include 

using namespace std;
const double pi = 4 * atan(1.0);
typedef long long ll;

ll solve (ll R) {
    ll ret = 0;

    ll r = R, M = R * R;
    for (ll i = 0; i <= R; i++) {
        while (r * r + i * i > M)
            r--;
        ret += r;
    }
    return 4 * ret + 1;
}

int main () {
    ll n;
    while (scanf("%lld", &n) == 1) {
        printf("%lld\n%lld\n", n, solve(n));
    }
    return 0;
}