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。
1 #include<iostream> 2 #include<cstdio> 3 #include<queue> 4 #include<cstring> 5 #include<algorithm> 6 #include<cmath> 7 #include<map> 8 #define lson l, m, rt<<1 9 #define rson m+1, r, rt<<1|1 10 #define INF 0x3f3f3f3f 11 typedef long long ll; 12 using namespace std; 13 ll a[100010], b[100010]; 14 double c[100010]; 15 ll n, m; 16 bool cmp(const double a, const double b) 17 { 18 return a>b; 19 } 20 int C(double x) 21 { 22 for(int i = 0; i < n; i++){ 23 c[i] = a[i]-x*b[i]; 24 } 25 sort(c, c+n, cmp);//降序 26 double ans=0; 27 for(int i = 0; i < n-m; i++){ 28 ans += c[i]; 29 } 30 return ans<=0;// 31 } 32 int main() 33 { 34 while(~scanf("%lld%lld", &n, &m)){ 35 if(!n&&!m) break; 36 for(int i = 0; i < n; i++){ 37 scanf("%lld", &a[i]); 38 } 39 for(int i = 0; i < n; i++){ 40 scanf("%lld", &b[i]); 41 } 42 double lb = 0, ub = 1; 43 for(int i = 0; i < 100; i++){ 44 //while(ub-lb>1e-6){ 45 double mid = (ub+lb)/2; 46 if(C(mid)){ 47 ub = mid; 48 } 49 else lb = mid; 50 //cout << mid << endl; 51 } 52 printf("%.0lf\n", (ub*100)); 53 } 54 return 0; 55 }
