hdu 4305 Lightning

http://acm.hdu.edu.cn/statistic.php?pid=4305&from=126&lang=&order_type=0

　　生成树计数加上极角排序，开始的时候忘记了计算过程中，数值会变成负数，所以wa了一次。生成树计数的矩阵运算必须注意，最后答案应该将它调整为整数。

　　题意是有n(n<=300)个人，如果某个人被电了，在他附近r范围内的人都会被电，算出被电的人形成的图案的种类数。两个能传递的人之间的直线位置不能有第三个人。

1800+ms的代码。。。囧：

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>

using namespace std;

const int maxn = 305;
const int maxSize = 305;
const int initMod = 10007;
const double eps = 1e-12;
int curSize = maxSize;

struct point {
    int x;
    int y;
    int id;

    bool operator == (point &a) const {
        return x == a.x && y == a.y;
    }
} pt[maxn], p0, buf[maxn];

int dis2(point &a, point &b) {
    int dx = a.x - b.x;
    int dy = a.y - b.y;

    return dx * dx + dy * dy;
}

bool cmp(point a, point b) {
    if (a == p0) return true;
    if (b == p0) return false;

    double tmp = atan2(a.y - p0.y, a.x - p0.x) - atan2(b.y - p0.y, b.x - p0.x);

    if (fabs(tmp) < eps) return dis2(a, p0) < dis2(b, p0);
    return tmp < 0;
}

struct Mat {
    int val[maxSize][maxSize];

    Mat () {
        for (int i = 0; i < curSize; i++) {
            for (int j = 0; j < curSize; j++) {
                val[i][j] = 0;
            }
        }
    }
    int det() {
        int ret = 1;

        for (int p = 1; p < curSize; p++) {
            for (int i = p + 1; i < curSize; i++) {
                while (val[i][p]) {
                    int k = val[p][p] / val[i][p];

                    for (int j = p; j < curSize; j++) {
                        val[p][j] = (val[p][j] - val[i][j] * (k % initMod)) % initMod;
                        swap(val[p][j], val[i][j]);
                    }
                    ret = -ret;
                }
            }
            ret *= val[p][p];
            ret = (ret % initMod + initMod) % initMod;
        }

        return ret;
    }
    void print() {
        for (int i = 0; i < curSize; i++) {
            for (int j = 0; j < curSize; j++) {
                printf("%d ", val[i][j]);
            }
            puts("");
        }
        puts("~~~");
    }
} mat;

void input(int n) {
    for (int i = 0; i < n; i++) {
        scanf("%d%d", &pt[i].x, &pt[i].y);
        pt[i].id = i;
        buf[i] = pt[i];
    }
}

bool diffLine(point &a, point &p, point &b) {
    return fabs(atan2(a.y - p.y, a.x - p.x) - atan2(b.y - p.y, b.x - p.x)) > eps;
}

void addEdge(int &a, int &b) {
    mat.val[a][b]--;
    mat.val[a][a]++;
}

void makeMat(int n, int r) {
    mat = Mat();
    for (int i = 0; i < n; i++) {
        p0 = buf[i];
        sort(pt, pt + n, cmp);
        if (dis2(pt[1], p0) <= r) {
            addEdge(pt[1].id, p0.id);
        }
        for (int j = 2; j < n; j++) {
            if (diffLine(pt[j - 1], p0, pt[j])) {
                if (dis2(pt[j], p0) <= r) {
                    addEdge(pt[j].id, p0.id);
                }
            }
        }
//        for (int j = 0; j < n; j++) {
//            printf("%d %d\n", pt[j].x, pt[j].y);
//        }
//        puts("~~~");
    }
//    mat.print();
//    puts("!!!");
}

bool vis[maxn];

void dfs(int x) {

    for (int i = 0; i < curSize; i++) {
        if (vis[i]) continue;
        if (mat.val[x][i]) {
            vis[i] = true;
            dfs(i);
        }
    }
}

bool check(int n) {
    memset(vis, false, sizeof(vis));
    vis[0] = true;
    dfs(0);
    for (int i = 0; i < n; i++) {
        if (!vis[i]) return false;
    }

    return true;
}

int main() {
    int T;
    int n, m;

//    freopen("in", "r", stdin);
    scanf("%d", &T);
    while (T--) {
        scanf("%d%d", &n, &m);
        curSize = n;
        input(n);
        makeMat(n, m * m);

        if (check(n)) {
            int ans = mat.det();

            printf("%d\n", ans);
        } else puts("-1");
    }

    return 0;
}

——written by Lyon