如题，#1299726 在 Gym 上（开文操）会 WA on 1，在 QOJ 上能 AC。建议修改为如下 SPJ（对着原题 Java 版改的）：

#include "testlib.h"
#include <algorithm>
#include <cmath>
#include <set>
#include <vector>
#define EPS 2e-3
#define MAX_C 1000000000

struct Edge
{
    int v;
    double l;
    int len;
    Edge(int v, double l, int len) : v(v), l(l), len(len) {}
    bool operator<(Edge that) const
    {
        if (l != that.l)
            return l < that.l;
        return v < that.v;
    }
};

int len;

double read(double w, int n, std::vector<double> x, std::vector<double> y, InStream &is, TResult type)
{
    len = 0;
    x[n] = is.readDouble();
    y[n] = is.readDouble();
    if (!is.seekEof())
        quitf(type, "Extra data in output file");
    if (x[n] < -EPS || w + EPS < x[n])
        quitf(_wa, "x = %.3lf outside of the river", x[n]);
    if (y[n] < -MAX_C || MAX_C + EPS < y[n])
        quitf(_wa, "y = %.3lf outside of allowed range", y[n]);
    std::set<Edge> edges;
    for (int i = 0; i <= n; ++i)
        edges.emplace(i, x[i] * x[i], 1);
    double minD = w * w / 4.0;
    double maxD = 0;
    std::vector<bool> u(n + 1);
    while (!edges.empty())
    {
        Edge e = *edges.begin();
        edges.erase(edges.begin());
        if (u[e.v])
        {
            continue;
        }
        if (e.l >= minD)
        {
            break;
        }
        maxD = std::max(maxD, e.l);
        if (minD >= (w - x[e.v]) * (w - x[e.v]))
        {
            minD = (w - x[e.v]) * (w - x[e.v]);
            len = e.len + 1;
        }
        minD = std::min(minD, (w - x[e.v]) * (w - x[e.v]));

        if (minD <= maxD)
        {
            break;
        }
        u[e.v] = true;
        for (int j = 0; j <= n; j++)
        {
            double d = (x[e.v] - x[j]) * (x[e.v] - x[j]) + (y[e.v] - y[j]) * (y[e.v] - y[j]);
            if (!u[j])
            {
                edges.emplace(j, d, e.len + 1);
            }
        }
    }
    return std::sqrt(std::max(minD, maxD));
}

int main(int argc, char *argv[])
{
    registerTestlibCmd(argc, argv);
    double w = inf.readInt();
    int n = inf.readInt();
    std::vector<double> x(n + 1), y(n + 1);
    for (int i = 0; i < n; ++i)
        x[i] = inf.readInt(), y[i] = inf.readInt();
    double ja = read(w, n, x, y, ans, _fail);
    double pa = read(w, n, x, y, ouf, _pe);
    if (std::abs(ja - pa) <= EPS)
    {
        quitf(_ok, "%.3lf, len = %d", ja, len);
    }
    TResult type = ja < pa ? _wa : _fail;
    quitf(type, "Expected %.3lf, found %.3lf", ja, pa);
}