hdu 2645 bfs

思路：将所有‘1’的点入队bfs一次即可。

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

typedef pair<int, int> pii;
const int N = 183;
char g[N][N];
int d[N][N];
int dx[] = { 0, 0, 1, -1 };
int dy[] = { 1, -1, 0, 0 };
int n, m;

bool ok( int x, int y )
{
    return x >= 0 && x < n && y >= 0 && y < m && d[x][y] == -1;
}

queue<pii> q;

void bfs()
{
    memset( d, -1, sizeof(d) );
    for ( int i = 0; i < n; i++ )
    {
        for ( int j = 0; j < m; j++ )
        {
            if ( g[i][j] == '1' )
            {
                q.push( make_pair( i, j ) );
                d[i][j] = 0;
            }
        }
    }
    while ( !q.empty() )
    {
        pii cur = q.front();
        q.pop();
        for ( int i = 0; i < 4; i++ )
        {
            int x = cur.first + dx[i];
            int y = cur.second + dy[i];
            if ( ok( x, y ) )
            {
                q.push( make_pair( x, y ) );
                d[x][y] = d[cur.first][cur.second] + 1;
            }
        }
    }
}

int main ()
{
    while ( scanf("%d%d", &n, &m) != EOF )
    {
        for ( int i = 0; i < n; i++ )
        {
            scanf("%s", g[i]);
        }
        bfs();
        for ( int i = 0; i < n; i++ )
        {
            for ( int j = 0; j < m; j++ )
            {
                printf("%d", d[i][j]);
                if ( j != m - 1 ) putchar(' ');
                else putchar('\n');
            }
        }
    }
    return 0;
}