UVA 572 Oil Deposits油田（DFS求連通塊）
Due to recent rains, water has pooled in various places in Farmer John's field, which is represented by a rectangle of N x M (1 <= N <= 100; 1 <= M <= 100) squares. Each square contains either water ('W') or dry land ('.'). Farmer John would like to figure out how many ponds have formed in his field. A pond is a connected set of squares with water in them, where a square is considered adjacent to all eight of its neighbors.
Given a diagram of Farmer John's field, determine how many ponds he has.
Input
* Line 1: Two space-separated integers: N and M
* Lines 2..N+1: M characters per line representing one row of Farmer John's field. Each character is either 'W' or '.'. The characters do not have spaces between them.
Output
* Line 1: The number of ponds in Farmer John's field.
Sample Input
10 12
W........WW.
.WWW.....WWW
....WW...WW.
.........WW.
.........W..
..W......W..
.W.W.....WW.
W.W.W.....W.
.W.W......W.
..W.......W.
Sample Output
3
Hint
OUTPUT DETAILS:
There are three ponds: one in the upper left, one in the lower left,and one along the right side.
題解：輸入m行n列的字符矩陣，統計字符“W”組成多少個八連塊。如果兩個字符“W”所在的格子相鄰（橫，豎或者對角線方向），就說它們屬於同一個八連塊，采用二重循環來找。
這就是連通塊原理；每訪問一次“W”，就給它寫上標記的編號，方便檢查。
AC代碼：
#include<cstdio>
#include<cstring>
const int maxn=1000+5;
char tu[maxn][maxn]; //輸入圖的數組
int m,n,idx[maxn][maxn]; //標記數組
void dfs(int r,int c,int id)
{
if(r<0||r>=m||c<0||c>=n)
return;
if(idx[r][c]>0||tu[r][c]!='W')
return;
idx[r][c]=id;
for(int dr=-1; dr<=1; dr++)
for(int dc=-1; dc<=1; dc++) // 尋找周圍八塊
if(dr!=0||dc!=0)
dfs(r+dr,c+dc,id);
}
int main()
{
int i,j;
while(scanf("%d%d",&m,&n)==2&&m&&n)
{
for(i =0; i<m; i++)
scanf("%s",tu[i]);
memset(idx,0,sizeof(idx));
int q=0;
for(i=0; i<m; i++)
for(j=0; j<n; j++)
if(idx[i][j]==0&&tu[i][j]=='W')
dfs(i,j,++q);
printf("%d\n",q);
}
return 0;
}
