poj-3072 Robot ***

/*
 * Graph-poj-3072.cpp
 *
 *  Created on: 2011-11-20
 *
 *  dijkstra..
 *
 *  分别用 STL 的 heap操作 和  普通的数组操作  实现
 *
 *
 */
#include <cstdio>
#include <cmath>
#include <cstring>
using namespace std;

const int maxn = 20 + 2;
const double pi = atan(1.0) * 4;
const double eps = 1e-9;
const double inf = 100000000;
int r, n;
bool vis[maxn] = {};

struct SNode{
    int x, y;
    double degree;
    double dist;
};
SNode node[maxn];

//两点连线和x轴的夹角
double getDegree(SNode *cur, SNode *next){
    int tmpx = next->x - cur->x;
    int tmpy = next->y - cur->y;
    double degree = atan2((double)tmpy, (double)tmpx);

//    if(degree < -eps) degree += 2 * pi;        //化为[0..2*pi]...这里可写可不写。

    return degree;
}

//从cur点的当前方向转到next点的角度， 注意不超过 pi
double rotateDegree(SNode *cur, SNode *next, double &degree){
    double nextDegree = getDegree(cur, next);
    degree = nextDegree;

    double ans = fabs(nextDegree - cur->degree);
    if(ans > pi + eps) ans = 2 * pi - ans;

    return ans;
}

//初始化
void ini(){
    memset(vis, 0, sizeof(vis));

    for(int i=0; i<n; i++){
        node[i].dist = inf;
    }
    node[0].dist = 0;
    node[0].degree = getDegree(&node[0], &node[n-1]);
}

//更新个点的dist域和degree域
void update(SNode *cur, SNode *next){
    double dist;
    double tmpDist = sqrt(fabs((cur->x - next->x) * (cur->x - next->x)*1.0
                        + (cur->y - next->y) * (cur->y - next->y)*1.0));

    //超过r
    if(tmpDist > r + eps)
        return;

    //
    double tmpDegree;
    //距离，注意角度化为 °
    dist = rotateDegree(cur, next, tmpDegree) * 180 / pi + tmpDist + cur->dist;
    if(dist < next->dist - eps){
        next->dist = dist;
        next->degree = tmpDegree;
    }
}


void dijkstra(){
    double min = inf;
    int cur = -1;

    ini();

    while(!vis[n-1]){
        //找到当前最小距离的点
        cur = -1, min = inf;
        for(int i=0; i<n; i++){
            if(!vis[i] && node[i].dist < min - eps){
                min = node[i].dist;
                cur = i;
            }
        }
        //更新完了
        if(cur == -1) break;

        vis[cur] = true;

        //更新
        for(int i=0; i<n; i++){
            if(vis[i]) continue;
            update(&node[cur], &node[i]);
        }
    }


    //结果
    if(!vis[n-1])
        printf("impossible\n");
    else
        printf("%d\n", (int)(node[n-1].dist + 0.5));

}



int main(){
    while(scanf("%d%d", &r, &n)){
        if(r == -1) return 0;

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

        dijkstra();
    }

    return 0;
}

　　

　　

//用 STL 的 heap

　　

/*
 * Graph-poj-3072.cpp
 *
 *  Created on: 2011-11-20
 */
#include <cstdio>
#include <cmath>
#include <vector>
#include <algorithm>
using namespace std;

const int maxn = 20 + 2;
const double pi = atan(1.0) * 4;
const double eps = 1e-9;
const double inf = 100000000;
int r, n;

struct SNode{
    int x, y;
    double degree;
    double dist;
};
SNode node[maxn];


//实现最小堆
bool cmp(SNode *lhs, SNode *rhs){
    return lhs->dist > (rhs->dist + eps);
}

double getDegree(SNode *cur, SNode *next){
    int tmpx = next->x - cur->x;
    int tmpy = next->y - cur->y;
    double degree = atan2((double)tmpy, (double)tmpx);
//    if(degree < -eps) degree += 2 * pi;

    return degree;
}


double rotateDegree(SNode *cur, SNode *next, double &degree){
    double nextDegree = getDegree(cur, next);
    degree = nextDegree;

    double ans = fabs(nextDegree - cur->degree);
    if(ans > pi + eps) ans = 2 * pi - ans;

    return ans;
}

void ini(vector<SNode *> &v){
    for(int i=0; i<n; i++){
        node[i].dist = inf;
        v.push_back(&node[i]);
    }
    node[0].dist = 0;
    node[0].degree = getDegree(&node[0], &node[n-1]);

    make_heap(v.begin(), v.end(), cmp);
}

bool update(SNode *cur, SNode *next){
    double dist;
    double tmpDist = sqrt(fabs((double)(cur->x - next->x) * (cur->x - next->x)
                        + (cur->y - next->y) * (cur->y - next->y)));

    if(tmpDist > r + eps)
        return false;

    bool flag = 0;
    double tmpDegree;
    dist = rotateDegree(cur, next, tmpDegree) * 180 / pi + tmpDist + cur->dist;
    if(dist < next->dist - eps){
        next->dist = dist;
        next->degree = tmpDegree;
        flag = 1;
    }
    return flag;
}

void dijkstra(){
    vector<SNode *> v;
    vector<SNode *>::iterator iter;
    ini(v);

    SNode *cur;
    while(!v.empty()){
        pop_heap(v.begin(), v.end(), cmp);
        cur = v.back();

        //何时退出循环。。。 这里WA了无数遍。。 囧
        if(cur->dist >= inf - eps) break;

        v.pop_back();

        for(iter=v.begin(); iter!=v.end(); iter++){
            update(cur, *iter);
        }
        //因为UPDATE了数据， 所以要重新建堆  （所以用heap操作慢一些。。 不如直接用数组）
        make_heap(v.begin(), v.end(), cmp);
    }


    if(node[n-1].dist >= inf - eps)
        printf("impossible\n");
    else
        printf("%d\n", (int)(node[n-1].dist + 0.5));

}



int main(){
    while(scanf("%d%d", &r, &n)){
        if(r == -1) return 0;

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

        dijkstra();
    }

    return 0;
}