Poj2386 Lake Counting （DFS）

Lake Counting

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 49414		Accepted: 24273

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

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.

#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;
char a[105][105];
int n,m;
void dfs(int x,int y)
{
    a[x][y]='.';
    for(int dx=-1;dx<=1;dx++){
        for(int dy=-1;dy<=1;dy++){
            int nx=x+dx,ny=y+dy;
            if(nx>=0&&nx<n&&ny>=0&&ny<m&&a[nx][ny]=='W'){
                dfs(nx,ny);
            }
        }
    }
    return ;
}
void solve()
{
    int res=0;
    for(int i=0;i<n;i++){
        for(int j=0;j<m;j++){
            if(a[i][j]=='W'){
                dfs(i,j);
                res++;
            }
        }
    }
    cout<<res<<endl;
}
int main()
{
    while(cin>>n>>m){
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                cin>>a[i][j];
            }
        } 
        solve();
    } 
    return 0;
}

 自己再熟悉一遍：

#include <iostream>
#include <cmath>
#include <algorithm>
#include <string>
#include <cstring>
using namespace std;
int n,m;
char a[105][105];
int res;
int nx,ny; 
void dfs(int x,int y)
{
    //八个方向搜索 
    for(int i=-1;i<=1;i++){
        for(int j=-1;j<=1;j++){
            nx=x+i,ny=y+j;
            if(nx>=0&&nx<n&&ny>=0&&ny<m&&a[nx][ny]=='W'){
                a[nx][ny]='.';
                dfs(nx,ny);
            }    
        }
    }
}
void solve()
{
    res=0;
    //每次从发现W的时候开始搜索由于一簇只能算一个地方所以res计数只加一次 
    for(int i=0;i<n;i++){
        for(int j=0;j<m;j++){
            if(a[i][j]=='W'){
                res++;
                dfs(i,j);
            }
        }
    }
}
int main()
{
    while(cin>>n>>m){
        memset(a,0,sizeof(a));
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                cin>>a[i][j];
            }
        }
        solve();
        cout<<res<<endl;
    }
    return 0;
}