hihocoder offer收割编程练习赛11 C 岛屿3

Posted 2020-09-06 王宜鸣

思路：

并查集的应用。

实现：

 1 #include <iostream>
 2 #include <cstdio>
 3 using namespace std;
 4 
 5 bool a[1005][1005];
 6 int n, x, y;
 7 int par[1000005];
 8 int ran[1000005];
 9 int dx[4] = { 1, 0, -1, 0 };
10 int dy[4] = { 0, 1, 0, -1 };
11 
12 void init(int n)
13 {
14     for (int i = 0; i < n; i++)
15     {
16         ran[i] = 0;
17         par[i] = i;
18     }
19 }
20 
21 int find(int x)
22 {
23     if (par[x] == x)
24         return x;
25     return par[x] = find(par[x]);
26 }
27 
28 
29 void unite(int x, int y)
30 {
31     x = find(x);
32     y = find(y);
33     if (x == y)
34         return;
35     if (ran[x] < ran[y])
36         par[x] = y;
37     else
38     {
39         par[y] = x;
40         if (ran[x] == ran[y])
41             ran[x]++;
42     }
43 }
44 
45 bool same(int x, int y)
46 {
47     return find(x) == find(y);
48 }
49 
50 int trans(int x, int y)
51 {
52     return x * 1000 + y;
53 }
54 
55 int main()
56 {
57     init(1000005);
58     cin >> n;
59     int now = 0, c = 0;
60     for (int i = 0; i < n; i++)
61     {
62         now++;
63         c += 4;
64         cin >> x >> y;
65         a[x][y] = true;
66         int tmp = trans(x, y);
67         for (int j = 0; j < 4; j++)
68         {
69             int nx = x + dx[j];
70             int ny = y + dy[j];
71             if (nx >= 0 && nx < 1000 && ny >= 0 && ny < 1000 && a[nx][ny])
72             {
73                 int t = trans(nx, ny);
74                 if (!same(tmp, t))
75                 {
76                     unite(tmp, t);
77                     now--;
78                 }
79                 c -= 2;
80             }
81         }
82         cout << now << " " << i + 1 << " " << c << endl;
83     }
84     return 0;
85 }