201312-5 I'm stuck!

思路

从起点正向深搜，检查是否可以达到终点，并标记从起点可到达的点。
从终点反向深搜，标记终点可以到达的点。
起点可到达而终点不可到达的点符合要求。

代码

#include <iostream>

#define MAXN (1<<6)

using namespace std;

// 左, 上, 右, 下 
int dx[4] = {0, -1, 0, 1};
int dy[4] = {-1, 0, 1, 0};

int Row, Col;
int sx, sy;
int tx, ty;
char map[MAXN][MAXN];
bool forward_dfs_visit[MAXN][MAXN];
bool back_dfs_visit[MAXN][MAXN];

void forward_dfs(int cur_row, int cur_col) {
	if (cur_row < 0 || cur_row > Row 
	 || cur_col < 0 || cur_col > Col 
	 || forward_dfs_visit[cur_row][cur_col] == true) {
		return;
	}
	int move_base, move_step;
	switch (map[cur_row][cur_col]) {
		case '+':
			move_base = 0, move_step = 1; 
			break;
		case '-':
			move_base = 0, move_step = 2;
			break;
		case '|':
			move_base = 1, move_step = 2;
			break;
		case '.':
			move_base = 3, move_step = 1;
			break;
		default:
			return;
	}
	forward_dfs_visit[cur_row][cur_col] = true;
	int i;
	for (i = move_base;i < 4;i += move_step) {
		forward_dfs(cur_row + dx[i],cur_col + dy[i]);
	}
}

void back_dfs(int cur_row, int cur_col) {
	if (cur_row < 0 || cur_row > Row 
	 || cur_col < 0 || cur_col > Col 
	 || back_dfs_visit[cur_row][cur_col] == true) {
		return;
	}
	back_dfs_visit[cur_row][cur_col] = true;
	int i;
	for (i = 0;i < 4;++i) {
		switch (map[cur_row + dx[i]][cur_col + dy[i]]) {
			case '+': 
				back_dfs(cur_row + dx[i],cur_col + dy[i]);
				break;
			case '-':
				if (i == 0 || i == 2) {
					back_dfs(cur_row + dx[i],cur_col + dy[i]);
				}
				break;
			case '|':
				if (i == 1 || i == 3) {
					back_dfs(cur_row + dx[i],cur_col + dy[i]);
				}
				break;
			case '.':
				if (i == 1) {
					back_dfs(cur_row + dx[i],cur_col + dy[i]);
				}
				break;
			default:
				continue;
		}
	}
}

int main() {
	
	int sx, sy;
	int tx, ty;	
	
	cin >> Row >> Col;
	int i, j;
	for (i = 0;i < Row;++i) {
		
		for (j = 0;j < Col;++j) {
			cin >> map[i][j];
			if (map[i][j] == 'S') {
				sx = i, sy = j;
			} else if (map[i][j] == 'T') {
				tx = i, ty = j;
			}
		}
	}
	
	map[sx][sy] = map[tx][ty] = '+';
	forward_dfs(sx,sy);
	
	if (forward_dfs_visit[tx][ty] == false) {
		cout << "I'm stuck!";
		return 0;
	}
	
	back_dfs(tx,ty);
	
	int block_cnt = 0;
	
	for (i = 0;i < Row;++i) {
		for (j = 0; j < Col;++j) {
			if (forward_dfs_visit[i][j] == true 
			&& back_dfs_visit[i][j] == false) {
				++block_cnt;
			}
		}
	}
	cout << block_cnt;
}