poj 3170

两遍bfs ~

#include <cstdio>
#include <cstdlib>
//#include <cmath>
#include <map>
#include <set>
#include <stack>
#include <vector>
#include <sstream>
#include <string>
#include <cstring>
#include <algorithm>
#include <iostream>
#define maxn 1010
#define INF 0x7fffffff
#define inf 10000000
#define ull unsigned long long
#define ll long long
using namespace std;
int g[maxn][maxn], m, n, vis[maxn][maxn], dis1[maxn][maxn], dis2[maxn][maxn], x1, x2, y1, y2;
int q[maxn*maxn];
int dx[] = {1 , 0, 0, -1}, dy[] = {0, 1, -1, 0};
void bfs1(int x, int y)
{
    int front = 0, rear = 0, u;
    vis[x][y] = 1;
    u = x*m+y;
    dis1[x][y] = 0;
    q[rear++] = u;
    while(front < rear)
    {
        u = q[front++];
        x = u/m, y = u%m;
        for(int i = 0; i < 4; ++ i)
        {
            int nx = x+dx[i], ny = y+dy[i];
            if(nx >= 0 && nx < n && ny >= 0 && ny < m && g[nx][ny] != 1 && !vis[nx][ny])
            {
                int v = nx*m+ny;
                q[rear++] = v;
                vis[nx][ny] = 1;
                dis1[nx][ny] = dis1[x][y]+1;
            }
        }
    }
//    puts("");
//    for(int i = 0; i < n; ++ i)
//    {
//        for(int j = 0 ; j < m; ++ j)
//        {
//            printf("%d ", dis1[i][j]);
//        }
//        puts("");
//    }
}
void bfs2(int x, int y)
{
    int front = 0, rear = 0, u;
    vis[x][y] = 1;
    u = x*m+y;
    dis2[x][y] = 0;
    q[rear++] = u;
    while(front < rear)
    {
        u = q[front++];
        x = u/m, y = u%m;
        for(int i = 0; i < 4; ++ i)
        {
            int nx = x+dx[i], ny = y+dy[i];
            if(nx >= 0 && nx < n && ny >= 0 && ny < m && g[nx][ny] != 1 && !vis[nx][ny])
            {
                int v = nx*m+ny;
                q[rear++] = v;
                vis[nx][ny] = 1;
                dis2[nx][ny] = dis2[x][y]+1;
            }
        }
    }
//    puts("");
//    for(int i = 0; i < n; ++ i)
//    {
//        for(int j = 0 ; j < m; ++ j)
//        {
//            printf("%d ", dis2[i][j]);
//        }
//        puts("");
//    }
}
void init()
{
    for(int i = 0; i < n; ++ i)
        for(int j = 0 ; j < m; ++ j)
        {
            dis1[i][j] = dis2[i][j] = inf;
        }
}
int main()
{
    while(scanf("%d%d", &m, &n) == 2)
    {
        init();
        for(int i = 0; i < n; ++ i)
            for(int j = 0 ; j < m; ++ j)
            {
                scanf("%d", &g[i][j]);
                if(g[i][j] == 2)
                    x1 = i, y1 = j;
                else if(g[i][j] == 3)
                    x2 = i, y2 = j;
            }
        memset(vis, 0, sizeof(vis));
        bfs1(x2, y2);
        memset(vis, 0, sizeof(vis));
        vis[x2][y2] = 1;
        bfs2(x1, y1);
        int ans = inf;
        for(int i = 0; i < n; ++ i)
            for(int j = 0 ; j < m; ++ j)
            {
                if(g[i][j] == 4)
                    ans = min(ans, dis1[i][j]+dis2[i][j]);
            }
        printf("%d\n", ans);
    }
    return 0;
}