poj1101

bfs

细节处理比较麻烦

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <queue>
using namespace std;

#define maxn 80

struct Node
{
    int x, y, turn, d;
};

bool map[maxn][maxn];
int vis[maxn][maxn];
int m, n;
int x1, y1, x2, y2;
int dir[4][2] =
{
{ 1, 0 },
{ 0, 1 },
{ -1, 0 },
{ 0, -1 } };

bool operator <(const Node &a, const Node &b)
{
    return a.turn > b.turn;
}

void input()
{
    getchar();
    n++;
    m++;
    memset(map, 0, sizeof(map));
    for (int i = 1; i < n; i++)
    {
        for (int j = 1; j < m; j++)
        {
            char ch = getchar();
            if (ch == 'X')
                map[i][j] = true;
        }
        getchar();
    }
}

bool ok(Node &a)
{
    if (a.x < 0 || a.y < 0 || a.x > n || a.y > m)
        return false;
    if (map[a.x][a.y])
        return false;
    if (vis[a.x][a.y] == -1)
        return true;
    return vis[a.x][a.y] >= a.turn;
}

void bfs(int t)
{
    priority_queue<Node> q;
    Node a;
    memset(vis, -1, sizeof(vis));
    for (int i = 0; i < 4; i++)
    {
        a.x = x1;
        a.y = y1;
        a.turn = 0;
        a.d = i;
        q.push(a);
    }
    vis[x1][y1] = true;
    bool tf = map[x2][y2];
    map[x2][y2] = false;
    while (!q.empty())
    {
        a = q.top();
        q.pop();
        if (a.x == x2 && a.y == y2)
        {
            printf("Pair %d: %d segments.\n", t, a.turn + 1);
            map[x2][y2] = tf;
            return;
        }
        for (int i = 0; i < 4; i++)
        {
            Node b;
            b.x = a.x + dir[i][0];
            b.y = a.y + dir[i][1];
            b.turn = a.turn;
            if (a.d != i)
                b.turn++;
            b.d = i;
            if (ok(b))
            {
                q.push(b);
                vis[b.x][b.y] = b.turn;
            }
        }
    }
    printf("Pair %d: impossible.\n", t);
    map[x2][y2] = tf;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    int t = 0;
    while (scanf("%d%d", &m, &n), n | m)
    {
        t++;
        printf("Board #%d:\n", t);
        input();
        int i = 0;
        while (scanf("%d%d%d%d", &y1, &x1, &y2, &x2), x1 | y1 | x2 | y2)
            bfs(++i);
        putchar('\n');
    }
    return 0;
}