POJ 3620 Avoid The Lakes, http://poj.org/problem?id=3620

POJ3620.c

/* POJ 3620 Avoid The Lakes, http://poj.org/problem?id=3620 */
#include <stdio.h>
#include <string.h>

/* N, M最大值是100，加一圈0可以防止越界 */
#define MAX 102

int N, M, K;
int map[MAX][MAX];

int count;

void dfs(int x, int y) {
    /* 加一圈0可以防止越界，因此不需要判断是否越界 */
    if (map[x][y] == 0) return;

    map[x][y] = 0;  /* 标记(x,y)已访问过，起到去重作用 */
    count++;
    dfs(x + 1, y);
    dfs(x - 1, y);
    dfs(x, y + 1);
    dfs(x, y - 1);
}

int main() {
    int i, j, max;
    memset(map, 0, sizeof(map));

    scanf("%d%d%d", &N, &M, &K);
    while (K--) {
        scanf("%d%d", &i, &j);
        map[i][j] = 1;
    }

    max = 0;
    for (i = 1; i <= N; i++) {
        for (j = 1; j <= M; j++) {
            if (map[i][j] == 1) {
                count = 0;
                dfs(i, j);
            }
            if (count > max) max = count;
        }
    }
    printf("%d\n", max);
    return 0;
}