hdu 4401 Battery

这里只给出代码，感兴趣的可以作以参考：

#include <algorithm>
#include <cstdio>
#include <cstring>
#include <string>
#include <queue>
#include <map>
#include <set>
#include <stack>
#include <ctime>
#include <functional>
#include <cmath>
#include <iostream>
#include <assert.h>
#pragma comment(linker, "/STACK:102400000,102400000")
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) < (b) ? (a) : (b))
#define mp std :: make_pair
#define st first
#define nd second
#define keyn (root->ch[1]->ch[0])
#define lson (u << 1)
#define rson (u << 1 | 1)
#define pii std :: pair<int, int>
#define pll pair<ll, ll>
#define pb push_back
#define type(x) __typeof(x.begin())
#define foreach(i, j) for(type(j)i = j.begin(); i != j.end(); i++)
#define FOR(i, s, t) for(int i = (s); i <= (t); i++)
#define ROF(i, t, s) for(int i = (t); i >= (s); i--)
#define dbg(x) std::cout << x << std::endl
#define dbg2(x, y) std::cout << x << " " << y << std::endl
#define clr(x, i) memset(x, (i), sizeof(x))
#define maximize(x, y) x = max((x), (y))
#define minimize(x, y) x = min((x), (y))
using namespace std;
typedef long long ll;
const int int_inf = 0x3f3f3f3f;
const ll ll_inf = 0x3f3f3f3f3f3f3f3f;
const int INT_INF = (int)((1ll << ) - );
const double double_inf = 1e30;
const double eps = 1e-;
const double pi = acos(-.);
typedef unsigned long long ul;
typedef unsigned int ui;
inline int readint() {
    int x;
    scanf("%d", &x);
    return x;
}
inline int readstr(char *s) {
    scanf("%s", s);
    return strlen(s);
}

class cmpt {
public:
    bool operator () (const int &x, const int &y) const {
        return x > y;
    }
};

int Rand(int x, int o) {
    //if o set, return [1, x], else return [0, x - 1]
    if (!x) return ;
    int tem = (int)((double)rand() / RAND_MAX * x) % x;
    return o ? tem +  : tem;
}
ll ll_rand(ll x, int o) {
    if (!x) return ;
    ll tem = (ll)((double)rand() / RAND_MAX * x) % x;
    return o ? tem +  : tem;
}

void data_gen() {
    srand(time());
    freopen("in.txt", "w", stdout);
    int kases = ;
    //printf("%d\n", kases);
    while (kases--) {
        int L = Rand(, ) + ;
        int n = Rand(L - , ) + ;
        int buf[], p = ;
        FOR(i, , n) buf[i] = Rand(L, );
        buf[++n] = , buf[++n] = L;
        sort(buf + , buf + n + );
        n = unique(buf + , buf + n + ) - buf - ;
        printf("%d %d\n", L, n);
        int t1 = Rand(, ) + ;
        int t2 = Rand(, ) + ;
        while (t2 == t1) {
            t2 = Rand(, ) + ;
        }
        if (t1 > t2) swap(t1, t2);
        printf("%d %d\n", t1, t2);
        FOR(i, , n) {
            printf("%d %d\n", buf[i], Rand(, ));
        }
        puts("\n");
    }
    puts("0 0");
}

const int maxn = 1e3 + ;
pii a[maxn];
int n, L;
int t1, t2;
struct Line {
    int lhs, rhs;
    double theta;
    int o;
    Line() {}
    Line(int _lhs, int _rhs, double _ta, int _o) {
        lhs = _lhs, rhs = _rhs, theta = _ta, o = _o;
    }
    bool operator < (const Line &other) {
        return theta > other.theta || theta == other.theta && rhs > other.rhs ||
            theta == other.theta && rhs == other.rhs && lhs > other.lhs;
    }
}lines[maxn * maxn];
int k;
double shadow, H;
bool inq[maxn];

double cal(double theta1, double theta2) {
    if (abs(theta1 - theta2) < eps) return ;
    double X = abs(theta1 - pi / ) < eps ?  : H / tan(theta1);
    double ret = (cos(theta2) - cos(theta1)) * (L - shadow + X) - H * (sin(theta1) - sin(theta2));
    shadow += abs(theta2) < eps ? L - shadow : H / tan(theta2) - X;
    return ret;
}

double solve(int l, int r) {
    shadow = H = ;
    k = ;
    FOR(i, , n) {
        inq[i] = ;
        H += a[i].nd;
        double mini = (double)ll_inf;
        int mk = ;
        ROF(j, i - , ) {
            double ang_tan = (double)a[i].second / (a[i].first - a[j].first);
            lines[k++] = Line(j, i, atan(ang_tan), );
            if (a[i].second <= a[j].second) break;
            ang_tan = (double)(a[i].second - a[j].second) / (a[i].first - a[j].first);
            lines[k++] = Line(j, i, atan(ang_tan), );
        }
    }
    double ang_l = pi /  * ( - l), ang_r = pi /  * ( - r);
    lines[k++] = Line(, , ang_l, ), lines[k++] = Line(, , ang_r, );
    sort(lines, lines + k);
    double ans = ;
    bool okay = false;
    double pre = pi / ;
    FOR(i, , k - ) {
        int o = lines[i].o;
        int lhs = lines[i].lhs, rhs = lines[i].rhs;
        double ang = lines[i].theta;
        double res = cal(pre, ang);
        if (okay) ans += res;
        if (o == ) break;
        else if (o == ) okay = true;
        else if (o ==  && inq[rhs]) inq[rhs] = , H -= a[rhs].nd, mk = ;
        else if (o ==  && inq[lhs]) H += a[rhs].nd - a[lhs].nd, inq[lhs] = , inq[rhs] = , mk = ;
        pre = ang;
    }
    return abs(ans *  / pi);
}

int main() {
    //data_gen(); return 0;
    //C(); return 0;
    int debug = ;
    if (debug) freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
    int kases = ;
    while (~scanf("%d%d", &L, &n) && n) {
        ++kases;
        t1 = readint(), t2 = readint();
        FOR(i, , n) scanf("%d%d", &a[i].st, &a[i].nd);
        double ans = ;
        if (t1 >= ) ans += solve(t1, t2);
        else {
            if (t2 > ) ans += solve(, t2), t2 = ;
            FOR(i, , n) a[i].first = L - a[i].st;
            FOR(i, , n / ) swap(a[i], a[n +  - i]);
            ans += solve( - t2,  - t1);
        }
        printf("%.5f\n", ans);
    }
    return ;
}