【洛谷】P2179 [NOI2012]骑行川藏

题解

感谢小迪给我讲题啊，这题小迪写挺好的我就不写了吧
小迪的题解

代码

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <ctime>
#include <vector>
#include <set>
//#define ivorysi
#define eps 1e-8
#define mo 974711
#define pb push_back
#define mp make_pair
#define pii pair<int,int>
#define fi first
#define se second
#define MAXN 10005
#define space putchar(' ')
#define enter putchar('\n')
using namespace std;
typedef long long int64;
typedef unsigned int u32;
typedef unsigned long long u64;
typedef double db;
const int64 MOD = 1000000007;
template<class T>
void read(T &res) {
    res = 0;char c = getchar();T f = 1;
    while(c < '0' || c > '9') {
    if(c == '-') f = -1;
    c = getchar();
    }
    while(c >= '0' && c <= '9') {
    res = res * 10 + c - '0';
    c = getchar();
    }
    res *= f;
}
template<class T>
void out(T x) {
    if(x < 0) putchar('-');
    if(x >= 10) {
    out(x / 10);
    }
    putchar('0' + x % 10);
}
int N;
db E,s[MAXN],k[MAXN],v[MAXN];
db getv(db x,int id) {
    db l = max(0.0,v[id]),r = 100000;
    int cnt = 50;
    db t = -1 / x;
    while(cnt--) {
    db mid = (l + r) / 2;
    if(mid * mid * (mid - v[id]) * 2 * k[id] <= t) l = mid;
    else r = mid;
    }
    return l;
}
db calc(db x) {
    db res = 0;
    for(int i = 1 ; i <= N ; ++i) {
    db t = getv(x,i);
    res += k[i] * s[i] * (t - v[i]) * (t - v[i]);
    }
    return res;
}
void Solve() {
    scanf("%d%lf",&N,&E);
    for(int i = 1 ; i <= N ; ++i) {
    scanf("%lf%lf%lf",&s[i],&k[i],&v[i]);
    }
    int cnt = 100;
    db L = -100000,R = 0;
    while(cnt--) {
    db MID = (L + R) / 2;
    if(calc(MID) <= E) L = MID;
    else R = MID;
    }
    db ans = 0;
    for(int i = 1 ; i <= N ; ++i) {
    ans += s[i] / getv(L,i);
    }
    printf("%.6lf\n",ans);
}
int main() {
#ifdef ivorysi
    freopen("f1.in","r",stdin);
#endif
    Solve();
    return 0;
}