HDU - 3533 Escape 【BFS】

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3533

需要注意的点：

1，人不能去有城堡的地方

2，子弹不能穿过城堡，遇到城堡子弹不会继续向前射，即使城堡在途中也不行，比如说子弹从(0, 0) 向 (0, 3)射，如果(0, 1)有城堡，子弹会消失。

3，子弹是从时间 t 开始射击的，不是从0开始。

思路就是人先走，然后遍历每一个城堡的射击时间，如果到了射击时间，就把这个城堡的子弹放入队列里面。然后注意一些限制条件即可。判断子弹是否在射击途中遇到城堡，如果没有就放入队列里面，弹出的子弹记得在那个位置减去一个子弹，表示这个子弹已经离开这个位置了。

#include <iostream>
#include <queue>
#include <cstring>
#include <string>
#include <map>
#include <cstdio>
#include <cmath>
#include <algorithm>

using namespace std;

const int INF = 0x3f3f3f3f;
const int Maxn = 4e5+10;

struct Shot {
    char dir;
    int i, j, v, t;
} shot[105];

struct Node {
    int i, j, step;
};

int N, M, gun, ener, dir[4][2] = { {1, 0}, {-1, 0},
{0, 1}, {0, -1} }, G[105][105];
bool vis[105][105];

void print() {
    for(int i = 0; i <= N; ++i) {
        for(int j = 0; j <= M; ++j)
            cout << G[i][j] << " ";
        cout << endl;
    }
    cout << endl;
}

void bfs() {
    memset(vis, 0, sizeof(vis));
    queue<Node> quP;
    queue<Shot> quS;
    Node Ntmp; Shot Stmp;
    Ntmp.i = 0; Ntmp.j = 0; Ntmp.step = 0;
    quP.push(Ntmp);
    vis[0][0] = true;

    while (!quP.empty()) {
        int cnt = quP.size(), curtime;
        while (cnt--) {
            Ntmp = quP.front(); quP.pop();
            curtime = Ntmp.step+1;

            if(Ntmp.i == N && Ntmp.j == M) {
                printf("%d\n", Ntmp.step); return;
            }

            for(int i = 0; i < 4; ++i) {
                Node now = Ntmp;
                now.i += dir[i][0]; now.j += dir[i][1];
                if(now.i < 0 || now.i > N || now.j < 0 || now.j > M
                   || vis[now.i][now.j] || G[now.i][now.j] == -1 || G[now.i][now.j] > 0) continue;
                now.step++;
                if(now.step > ener) continue;
                vis[now.i][now.j] = true;
                quP.push(now);
            }
            if(Ntmp.step+1 < ener && G[Ntmp.i][Ntmp.j] == 0) {
                Ntmp.step++; quP.push(Ntmp);
            }
        }

        for(int i = 0; i < gun; ++i)
            if(curtime % shot[i].t == 0) quS.push(shot[i]);

        cnt = quS.size();
        while(cnt--) {
            Stmp = quS.front(); quS.pop();
            if(G[Stmp.i][Stmp.j] > 0)
                G[Stmp.i][Stmp.j]--;

            Shot now = Stmp;
            if(now.dir == 'N' && now.i-now.v >= 0) {
                now.i -= now.v;
                bool ok = true;
                for(int i = Stmp.i-1; i >= now.i; --i) if(G[i][now.j] == -1) ok = false;
                if(ok) {
                    G[now.i][now.j]++;
                    quS.push(now);
                }
            }
            now = Stmp;
            if(now.dir == 'S' && now.i+now.v <= N) {
                now.i += now.v;
                bool ok = true;
                for(int i = Stmp.i+1; i <= now.i; ++i) if(G[i][now.j] == -1) ok = false;
                if(ok) {
                    G[now.i][now.j]++;
                    quS.push(now);
                }
            }
            now = Stmp;
            if(now.dir == 'W' && now.j-now.v >= 0) {
                now.j -= now.v;
                bool ok = true;
                for(int j = Stmp.j-1; j >= now.j; --j) if(G[now.i][j] == -1) ok = false;
                if(ok) {
                    G[now.i][now.j]++;
                    quS.push(now);
                }
            }
            now = Stmp;
            if(now.dir == 'E' && now.j+now.v <= M) {
                now.j += now.v;
                bool ok = true;
                for(int j = Stmp.j+1; j <= now.j; ++j) if(G[now.i][j] == -1) ok = false;
                if(ok) {
                    G[now.i][now.j]++;
                    quS.push(now);
                }
            }
        }
       // print();
    }
    printf("Bad luck!\n");
}

int main(void)
{
    while(scanf("%d%d%d%d", &N, &M, &gun, &ener) != EOF) {
        memset(G, 0, sizeof(G));
        for(int i = 0; i < gun; ++i) {
            scanf(" %c%d%d%d%d", &shot[i].dir,
                  &shot[i].t, &shot[i].v, &shot[i].i, &shot[i].j);
            G[shot[i].i][shot[i].j] = -1;
        }
       // print();
        bfs();
    }
	return 0;
}