DFS(连通块) ZOJ 2743 Bubble Shooter

题目传送门

题意：从炮台射出一个球，三个及以上颜色相同的会掉落，问最后会掉落多少个球

分析：先从炮台找一个连通块，然后与顶部连接的连通块都不会掉落，剩下的就是炮台射出后跟随掉落的。

#include <bits/stdc++.h>

const int N = 100 + 5;
char str[N][N];
int H, W, h, w;
int ans;

bool check(int x, int y) {
	if (x < 1 || x > H || y < 1 || y > W || (x%2==0 && y==W) || str[x][y] == '@') return false;
	return true;
}

void DFS(int x, int y, char color, int &cnt) {
	if (!check (x, y)) {
		return ;
	}
	if (color != '@' && color != str[x][y]) {
		return ;
	}
	cnt++;
	str[x][y] = '@';
	DFS (x - 1, y, color, cnt);
	DFS (x + 1, y, color, cnt);
	DFS (x, y - 1, color, cnt);
	DFS (x, y + 1, color, cnt);
	if (x & 1) {
		DFS (x - 1, y - 1, color, cnt);
		DFS (x + 1, y - 1, color, cnt);
	} else {
		DFS (x - 1, y + 1, color, cnt);
		DFS (x + 1, y + 1, color, cnt);
	}
}

int main() {
	while (scanf ("%d%d%d%d", &H, &W, &h, &w) == 4) {
        for (int i=1; i<=H; ++i) {
			scanf ("%s", str[i] + 1);
			for (int j=1; j<=W; ++j) {
				if (str[i][j] == 'E') {
					str[i][j] = '@';
				}
			}
        }
		int cnt = 0;
		DFS (h, w, str[h][w], cnt);
		int ans = cnt;
		if (ans < 3) {
			puts ("0");
			continue;
		}
		for (int i=1; i<=W; ++i) {
			DFS (1, i, '@', cnt);
		}
		for (int i=1; i<=H; ++i) {
			for (int j=1; j<=W; ++j) {
				if (i % 2 == 0 && j == W) continue;
				if (str[i][j] != '@') {
					ans++;
				}
			}
		}
		printf ("%d\n", ans);
	}

	return 0;
}