poj3626

bfs

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

#define maxx 1005
#define inc 502
#define maxn maxx * maxx

struct Point
{
int x, y;
} q[maxx * maxx];

int n, cx, cy;
bool vis[maxx][maxx];
bool map[maxx][maxx];
int dist[maxx][maxx];
int dir[4][2] =
{
{ 0, 1 },
{ 1, 0 },
{ 0, -1 },
{ -1, 0 } };

bool ok(Point &a)
{
if (a.x < 0 || a.y < 0 || a.x >= maxx || a.y >= maxx)
return false;
return !vis[a.x][a.y] && !map[a.x][a.y];
}

int bfs()
{
int front = 0;
int rear = 1;
q[0].x = inc;
q[0].y = inc;
memset(vis, 0, sizeof(vis));
vis[inc][inc] = true;
dist[inc][inc] = 0;
while (front != rear)
{
Point a = q[front++];
if (front == maxn)
front = 0;
for (int i = 0; i < 4; i++)
{
Point b;
b.x = a.x + dir[i][0];
b.y = a.y + dir[i][1];
if (ok(b))
{
q[rear++] = b;
if (rear == maxn)
rear = 0;
dist[b.x][b.y] = dist[a.x][a.y] + 1;
vis[b.x][b.y] = true;
if (b.x == cx && b.y == cy)
return dist[b.x][b.y];
}
}
}
return -1;
}

int main()
{
//freopen("t.txt", "r", stdin);
scanf("%d%d%d", &cx, &cy, &n);
cx += inc;
cy += inc;
memset(map, 0, sizeof(map));
for (int i = 0; i < n; i++)
{
int a, b;
scanf("%d%d", &a, &b);
a += inc;
b += inc;
map[a][b] = true;
}
int ans = bfs();
printf("%d\n", ans);
return 0;
}

转载于:https://www.cnblogs.com/rainydays/archive/2011/07/13/2105053.html