poj 3620 Avoid The Lakes 【DFS】

Avoid The Lakes

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 6998		Accepted: 3723

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 and M (1 ≤ M ≤ 100) columns. Each cell in the grid is either dry or submerged, and exactly K (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 and C

Output

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

Sample Input

3 4 5
3 2
2 2
3 1
2 3
1 1

Sample Output

4

题意：有一个N*M的图，现在知道了k个湖所在坐标即一个单元格（有的湖会连在一起成为 一个更大的湖），问你最大的湖占多少单元格。

基础DFS

AC代码：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
int N, M, K;
int Map[110][110];
int ans, sum;
void getMap()
{
    int a, b;
    while(K--)
    {
        scanf("%d%d", &a, &b);
        Map[a][b] = 1;
    }
}
int move[4][2] = {0,1, 0,-1, 1,0, -1,0};
bool judge(int x, int y)
{
    return x >= 1 && x <= N && y >=1 && y <= M && Map[x][y];
}
void DFS(int x, int y)
{
    sum++;
    Map[x][y] = 0;
    for(int i = 0; i < 4; i++)
    {
        int next_x = x + move[i][0];
        int next_y = y + move[i][1];
        if(judge(next_x, next_y))
            DFS(next_x, next_y);
    }
}
int main()
{
    while(scanf("%d%d%d", &N, &M, &K) != EOF)
    {
        memset(Map, 0, sizeof(Map));
        getMap();
        ans = 0;
        for(int i = 1; i <= N; i++)
        {
            for(int j = 1; j <= M; j++)
            {
                if(Map[i][j])
                {
                    sum = 0;
                    DFS(i, j);
                    ans = max(ans, sum);
                }
            }
        }
        printf("%d\n", ans);
    }
    return 0;
}