DFS/BFS Codeforces Round #301 (Div. 2) C. Ice Cave

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mob604756e5d059 2015-05-01 19:05:00

文章标签 #include ios 5e 搜索数值题解学习笔记编程语言 文章分类 代码人生

 1 /*
 2     题意：告诉起点终点，踩一次, '.'变成'X'，再踩一次，冰块破碎，问是否能使终点冰破碎
 3     DFS：如题解所说，分三种情况：1. 如果两点重合，只要往外走一步再走回来就行了；2. 若两点相邻，
 4         那么要不就是踩一脚就破了或者踩一脚走开再走回来踩一脚破了；3. 普通的搜索看是否能到达，
 5         若能还是要讨论终点踩几脚的问题:)
 6     DFS 耗时大，险些超时，可以用BFS来做
 7 */
 8 #include <cstdio>
 9 #include <algorithm>
10 #include <cstring>
11 #include <string>
12 #include <iostream>
13 using namespace std;
14 
15 const int MAXN = 5e2 + 10;
16 const int INF = 0x3f3f3f3f;
17 int n, m;
18 int sx, sy, ex, ey;
19 char maze[MAXN][MAXN];
20 bool vis[MAXN][MAXN];
21 int dx[4] = {1, -1, 0, 0};
22 int dy[4] = {0, 0, -1, 1};
23 
24 void DFS(int x, int y)
25 {
26     vis[x][y] = true;
27     if (maze[x][y] == 'X')    return ;
28 
29     for (int i=0; i<4; ++i)
30     {
31         int tx = x + dx[i];
32         int ty = y + dy[i];
33 
34         if (tx <= n && tx >= 1 && ty <= m && ty >= 1 && !vis[tx][ty])
35         {
36             DFS (tx, ty);
37         }
38     }
39 
40     return ;
41 }
42 
43 int main(void)        //Codeforces Round #301 (Div. 2) C. Ice Cave
44 {
45     //freopen ("C.in", "r", stdin);
46 
47     while (scanf ("%d%d", &n, &m) == 2)
48     {
49         memset (vis, 0, sizeof (vis));
50         for (int i=1; i<=n; ++i)
51         {
52             scanf ("%s", maze[i]+1);
53         }
54         scanf ("%d%d", &sx, &sy);
55         scanf ("%d%d", &ex, &ey);
56 
57         int cnt = 0;    bool flag = false;
58         for (int i=0; i<4; ++i)
59         {
60             int tx = ex + dx[i];
61             int ty = ey + dy[i];
62             if (tx == sx && ty == sy)    flag = true;
63             if (tx <= n && tx >= 1 && ty <= m && ty >= 1 && maze[tx][ty] == '.')    cnt++;
64         }
65 
66         if (sx == ex && sy == ey)
67         {
68             if (cnt >= 1)    puts ("YES");
69             else puts ("NO");
70         }
71         else if (flag)
72         {
73             if (maze[ex][ey] == 'X')    puts ("YES");
74             else
75             {
76                 if (cnt >= 1)    puts ("YES");
77                 else    puts ("NO");
78             }
79         }
80         else
81         {
82             maze[sx][sy] = '.';
83             DFS (sx, sy);
84             if (vis[ex][ey])
85             {
86                 if (maze[ex][ey] == 'X')    puts ("YES");
87                 else if (cnt >= 2)    puts ("YES");
88                 else    puts ("NO");
89             }
90             else    puts ("NO");
91         }
92     }
93 
94     return 0;
95 }

 1 #include <cstdio>
 2 #include <algorithm>
 3 #include <cstring>
 4 #include <queue>
 5 #include <string>
 6 #include <iostream>
 7 using namespace std;
 8 
 9 const int MAXN = 5e2 + 10;
10 const int INF = 0x3f3f3f3f;
11 int n, m;
12 int sx, sy, ex, ey;
13 char maze[MAXN][MAXN];
14 bool vis[MAXN][MAXN];
15 int dx[4] = {1, -1, 0, 0};
16 int dy[4] = {0, 0, -1, 1};
17 
18 bool BFS(void)
19 {
20     queue<pair<int, int> > Q;
21     Q.push (make_pair (sx, sy));
22 
23     while (!Q.empty ())
24     {
25         int x = Q.front ().first;    int y = Q.front ().second;    Q.pop ();
26         for (int i=0; i<4; ++i)
27         {
28             int tx = x + dx[i];
29             int ty = y + dy[i];
30 
31             if (tx == ex && ty == ey)    return true;
32 
33             if (tx <= n && tx >= 1 && ty <= m && ty >= 1 && maze[tx][ty] == '.')
34             {
35                 maze[tx][ty] = 'X';
36                 Q.push (make_pair (tx, ty));
37             }
38         }
39     }
40 
41     return false;
42 }
43 
44 int main(void)        //Codeforces Round #301 (Div. 2) C. Ice Cave
45 {
46     //freopen ("C.in", "r", stdin);
47 
48     while (scanf ("%d%d", &n, &m) == 2)
49     {
50         memset (vis, 0, sizeof (vis));
51         for (int i=1; i<=n; ++i)
52         {
53             scanf ("%s", maze[i]+1);
54         }
55         scanf ("%d%d", &sx, &sy);
56         scanf ("%d%d", &ex, &ey);
57 
58         int cnt = 0;    bool flag = false;
59         for (int i=0; i<4; ++i)
60         {
61             int tx = ex + dx[i];
62             int ty = ey + dy[i];
63             if (tx == sx && ty == sy)    flag = true;
64             if (tx <= n && tx >= 1 && ty <= m && ty >= 1 && maze[tx][ty] == '.')    cnt++;
65         }
66 
67         if (sx == ex && sy == ey)
68         {
69             if (cnt >= 1)    puts ("YES");
70             else puts ("NO");
71         }
72         else if (flag)
73         {
74             if (maze[ex][ey] == 'X')    puts ("YES");
75             else
76             {
77                 if (cnt >= 1)    puts ("YES");
78                 else    puts ("NO");
79             }
80         }
81         else
82         {
83             maze[sx][sy] = '.';
84             //DFS (sx, sy);
85             if (BFS () == true)
86             {
87                 if (maze[ex][ey] == 'X')    puts ("YES");
88                 else if (cnt >= 2)    puts ("YES");
89                 else    puts ("NO");
90             }
91             else    puts ("NO");
92         }
93     }
94 
95     return 0;
96 }