poj3620 avoid the lakes【dfs】

Avoid The Lakes

Time Limit : 2000/1000ms (Java/Other)   Memory Limit : 131072/65536K (Java/Other)

Total Submission(s) : 117   Accepted Submission(s) : 64

Problem Description

Farmer John's farm was flooded in the most recent storm, a fact only aggravated by the information that his cows are deathly afraid of water. His insurance agency will only repay him, however, an amount depending on the size of the largest "lake" on his farm.

The farm is represented as a rectangular grid with N (1 ≤ N ≤ 100) rows andM (1 ≤M ≤ 100) columns. Each cell in the grid is either dry or submerged, and exactlyK (1 ≤K ≤ N × M) of the cells are submerged. As one would expect, a lake has a central cell to which other cells connect by sharing a long edge (not a corner). Any cell that shares a long edge with the central cell or shares a long edge with any connected cell becomes a connected cell and is part of the lake.

 

Input

* Line 1: Three space-separated integers: N, M, and K
* Lines 2..K+1: Line i+1 describes one submerged location with two space separated integers that are its row and column:R andC

 

Output

* Line 1: The number of cells that the largest lake contains.　

 

Sample Input

3 4 53 22 23 12 31 1

 

Sample Output

4
 
题目大意：一个农村有n*m个方块，有的湿有的干，湿润的土地的块数为k，相邻的湿地可以构成一大块湿地
，给出湿地所对应的坐标，求最大的一块湿地有几个湿润的方块组成。
 
【代码】
#include<stdio.h>int a[110][110]={0};int num;int dx[4]={0,1,-1,0};int dy[4]={1,0,0,-1};int dfs(int x,int y){if(a[x][y]==1){a[x][y]=-1;num++;for(int i=0;i<4;i++){int nx=x+dx[i];int ny=y+dy[i];dfs(nx,ny);}}}int main(){int n,m,k,x,y,i,j,max=0;scanf("%d%d%d",&n,&m,&k);for(i=0;i<k;i++){scanf("%d%d",&x,&y);a[x][y]=1;}for(i=1;i<=n;i++)  for(j=1;j<=m;j++)  {    num=0;    dfs(i,j);    if(num>max)       max=num;  }  printf("%d\n",max);  return 0;}