POJ 3757

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cost=sigma(fi*ci)

vi=pi*bi/(pi+bi);

sigma(vi)*t=F;

fi=vi*t;

cost=simga(ci*fi)=sigma(ci*vi*t)=sigma(ci*vi)*t=sigma(ci*vi)*F/(sigma(vi)) 分数规划

此题优化后的二分居然只比迭代慢20ms 以下是迭代的代码

#include<cstdio>#include<cstring>#include<algorithm>#include<cmath>using namespace std;const int maxn = 211111;const double eps = 1e-6;typedef long long LL;struct node {double w, v, val;node() {}node(double w, double v) :w(w), v(v) {val = 0;}bool operator<(const node& t) const {return val < t.val;}} f[maxn];double F;int main() {int n, k, i;double w, p, b, v, c;scanf("%d%d%lf", &n, &k, &F);for (i = 0; i < n; ++i) {scanf("%lf%lf%lf", &p, &b, &c);v = (p * b) / (p + b);f[i] = node(v * c * F, v);}double rate = 0, pre = -100;rate = f[0].w / f[0].v;for (i = 0; i < n; ++i)f[i].val = f[i].w - f[i].v * rate;while (fabs(rate - pre) > eps) {pre = rate;w = v = 0;sort(f, f + n);for (i = 0; i < k; ++i)w += f[i].w, v += f[i].v;rate = w / v;for (i = 0; i < n; ++i)f[i].val = f[i].w - f[i].v * rate;}printf("%.4f\n", rate);return 0;}