poj2976 Dropping tests（01分数规划 好题）

https://vjudge.net/problem/POJ-2976

又是一波c++AC,g++WA的题。。

先推导公式：由题意得 Σa[i]/Σb[i]<=x，二分求最大x。化简为Σ(a[i]-x*b[i])<=0，按a[i]-x*b[i]降序排列，从中取前n-m个和满足该式的话，就说明x多半是偏大了。

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<map>
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
#define INF 0x3f3f3f3f
typedef long long ll;
using namespace std;
ll a[100010], b[100010];
double c[100010];
ll n, m;
bool cmp(const double a, const double b)
{
    return a>b;
}
int C(double x)
{
    for(int i = 0; i < n; i++){
        c[i] = a[i]-x*b[i];
    }
    sort(c, c+n, cmp);//降序 
    double ans=0;
    for(int i = 0; i < n-m; i++){
        ans += c[i];
    }
    return ans<=0;//
}
int main()
{
    while(~scanf("%lld%lld", &n, &m)){
        if(!n&&!m) break;
        for(int i = 0; i < n; i++){
            scanf("%lld", &a[i]);
        }
        for(int i = 0; i < n; i++){
            scanf("%lld", &b[i]);
        }
        double lb = 0, ub = 1;
        for(int i = 0; i < 100; i++){ 
        //while(ub-lb>1e-6){
            double mid = (ub+lb)/2;
            if(C(mid)){
                ub = mid;
            }
            else lb = mid;
            //cout << mid << endl;
        }
        printf("%.0lf
", (ub*100));
    } 
    return 0;
}