Submission #888108

#	Time	Username	Problem	Language	Result	Execution time	Memory
888108		eysbutno	Mobile (BOI12_mobile)	C++11	0 / 100	1066 ms	59068 KiB

mobile

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
#define all(x) begin(x), end(x)
#define ckmax(a, b) a = max(a, b)
#define ckmin(a, b) a = min(a, b)
#define pb push_back
#define ins insert
#define f first 
#define s second 

int main() {
    cin.tie(0) -> sync_with_stdio(0);
    int n, l; 
    cin >> n >> l;
    vector<pii> loc(n);
    for (auto& i : loc) {
        cin >> i.f >> i.s;
    }
    auto len = [&](ld d, ld y) {
        return sqrt(pow(d, 2) - pow(y, 2));
    };
    auto check = [&](ld d) {
        vector<pair<ld, ld>> itvs;
        for (int i = 0; i < n; i++) {
            int x = loc[i].f,
                y = loc[i].s;
            if (y > d) continue;
            ld dx = len(d, y);
            itvs.pb({x - dx, x + dx});
        }
        sort(all(itvs));
        if (itvs[0].f > 0) {
            return false;
        }
        ld far = itvs[0].f;
        for (auto& i : itvs) {
            if (i.f > far) {
                return false;
            }
            ckmax(far, i.s);
        }
        return far >= l;
    };
    ld low = 0, high = 3e9, 
        prec = 1e-7, ans = -1;
    while (low <= high) {
        ld mid = (low + high) / 2;
        if (check(mid)) {
            ans = mid;
            high = mid - prec;
        } else {
            low = mid + prec;
        }
    }
    cout << setprecision(7);
    cout << low << '\n';
}
/**
 * WHY DECIMAL PRECISION??
 * 
 * Binary search the minimum
 * distance needed to cover the
 * highway. That's the answer.
*/

Compilation message (stderr)

mobile.cpp: In function 'int main()':
mobile.cpp:48:22: warning: variable 'ans' set but not used [-Wunused-but-set-variable]
   48 |         prec = 1e-7, ans = -1;
      |                      ^~~

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