poj2312

priority_queue的bfs

priority_queue的bfs相当于使用了dijkstra的思想。

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

#define maxn 305

struct Point
{
    int x, y, w;
}s, t;

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

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

void input()
{
    for (int i = 0; i < n; i++)
        scanf("%s", map[i]);
}

void work()
{
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++)
        {
            if (map[i][j] == 'Y')
            {
                s.x = i;
                s.y = j;
                s.w = 0;
                map[i][j] = 'E';
            }
            if (map[i][j] == 'T')
            {
                t.x = i;
                t.y = j;
                map[i][j] = 'E';
            }
        }
}

bool ok(Point a, int &step)
{
    if (a.x < 0 || a.y < 0 || a.x >= n || a.y >= m)
        return false;
    if (vis[a.x][a.y])
        return false;
    if (map[a.x][a.y] == 'S' ||map[a.x][a.y] == 'R')
        return false;
    if (map[a.x][a.y] == 'E')
    {
        step = 1;
        return true;
    }
    step = 2;
    return true;
}

int bfs()
{
    priority_queue <Point> pq;
    memset(vis, 0, sizeof(vis));
    pq.push(s);
    vis[s.x][s.y] = true;
    while (!pq.empty())
    {
        Point u = pq.top();
        pq.pop();
        if (u.x == t.x && u.y == t.y)
            return u.w;
        Point v;
        for (int i = 0; i < 4; i++)
        {
            v.x = u.x + dir[i][0];
            v.y = u.y + dir[i][1];
            int step;
            if (ok(v, step))
            {
                v.w = u.w + step;
                pq.push(v);
                vis[v.x][v.y] = true;
            }
        }
    }
    return -1;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (scanf("%d%d", &n, &m), n | m)
    {
        input();
        work();
        printf("%d\n", bfs());
    }
    return 0;
}