poj2935

bfs

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

#define maxn 8

struct Wall
{
    int s, e;
    int p;
    bool h;
}wall[5];

struct Point
{
    int x, y;
}s, e, q[maxn * maxn];

int n = 6;
int step[maxn][maxn];
int from[maxn][maxn];
int dir[4][2] = {{1, 0},{0, 1},{-1, 0},{0, -1}};

void input()
{
    scanf("%d%d", &e.x, &e.y);
    for (int i = 0; i < 3; i++)
    {
        int a, b, c, d;
        scanf("%d%d%d%d", &a, &b, &c, &d);
        if (a > c)
            swap(a, c);
        if (b > d)
            swap(b, d);
        if (a == c)
        {
            wall[i].h = false;
            wall[i].s = b + 1;
            wall[i].e = d;
            wall[i].p = a;
        }
        else
        {
            wall[i].h = true;
            wall[i].s = a + 1;
            wall[i].e = c;
            wall[i].p = b;
        }
    }
}

bool ok(Point &a)
{
    if (a.x < 1 || a.y < 1 || a.x > n || a.y > n)
        return false;
    return step[a.x][a.y] == -1;
}

bool cross(Point a, Point b)
{
    if (a.x > b.x)
        swap(a, b);
    if (a.y > b.y)
        swap(a, b);
    bool h;
    int s, p;
    if (a.x == b.x)
    {
        h = false;
        s = a.y;
        p = a.x;
    }
    else
    {
        h = true;
        s = a.x;
        p = a.y;
    }
    for (int i = 0; i < 3; i++)
        if (wall[i].h != h && wall[i].p == s && p <= wall[i].e && p >= wall[i].s)
            return true;
    return false;
}

void bfs()
{
    memset(step, -1, sizeof(step));
    memset(from, -1, sizeof(from));
    step[s.x][s.y] = 0;
    q[0].x = s.x;
    q[0].y = s.y;
    int front = 0;
    int rear = 1;
    while (front != rear)
    {
        Point a = q[front++];
        Point b;
        for (int i = 0; i < 4; i++)
        {
            b.x = a.x + dir[i][0];
            b.y = a.y + dir[i][1];
            if (ok(b) && !cross(a, b))
            {
                q[rear++] = b;
                step[b.x][b.y] = step[a.x][a.y] + 1;
                from[b.x][b.y] = i;
                if (b.x == e.x && b.y == e.y)
                    return;
            }
        }
    }
}

void print()
{
    int x = e.x;
    int y = e.y;
    int stk[maxn * maxn];
    int top = 0;
    while (from[x][y] != -1)
    {
        stk[top++] = from[x][y];
        int a, b;
        a = x - dir[from[x][y]][0];
        b = y - dir[from[x][y]][1];
        x = a;
        y = b;
    }
    char st[10] = "ESWN";
    for (int i = top - 1; i >= 0; i--)
        putchar(st[stk[i]]);
    putchar('\n');
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (scanf("%d%d", &s.x, &s.y), s.x | s.y)
    {
        input();
        bfs();
        print();
    }
    return 0;
}