bool check(double x) {/* ... */} // 检查x是否满足某种性质 double bsearch_3(double l, double r) { const double eps = 1e-6; // eps 表示精度,取决于题目对精度的要求 while (r - l > eps) { double mid = (l + r) / 2; if (check(mid)) r = mid; else l = mid; } return l; }