Lake Counting(DFS)
2014-07-27 11:28
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Description
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
Sample Output
Hint
OUTPUT DETAILS:
There are three ponds: one in the upper left, one in the lower left,and one along the right side.
解题思路
不用visa[]标识数组,因为一个W点只会被用到一次,用过后改掉就好,相当于标记,一直搜到底,搜完一层回到上一层,(没有不满足条件的情况中途回溯)
AC代码
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.
解题思路
不用visa[]标识数组,因为一个W点只会被用到一次,用过后改掉就好,相当于标记,一直搜到底,搜完一层回到上一层,(没有不满足条件的情况中途回溯)
AC代码
<pre name="code" class="html">#include <stdio.h> #include <string.h> int n,m,cnt; char map[150][150]; int add[8][2] = { {1,0},{0,1},{-1,0},{0,-1},{1,1},{-1,1},{-1,-1},{1,-1} }; void dfs(int i,int j) { map[i][j]='#'; for(int k=0; k<8; k++) { int x=i+add[k][0]; int y=j+add[k][1]; if(x<n && y<m && x>=0 && y>=0 && map[x][y] == 'W') dfs(x,y); } } int main() { int i,j; scanf("%d%d",&n,&m); getchar(); for(i=0; i<n; i++) scanf("%s",map[i]); cnt=0; for(i=0; i<n; i++) for(j=0; j<m; j++) if(map[i][j]=='W') { cnt++; dfs(i,j); } printf("%d\n",cnt); return 0; }
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