USACO March. 2012

Connect the Cows

Times17

水题

Landscaping

Flowerpot

Tractor

广搜 搜到边界就可以终止了 没什么难度

#include <stdio.h>

#include <string.h>

#include <queue>

using namespace std;

const int MAX = 1010;

int a[MAX][MAX];

int dir[4][2] = {0,1,0,-1,1,0,-1,0};

struct node

{

	int x;

	int y;

	int step;

	bool friend operator < (node a,node b)

	{

		return a.step > b.step;

	}

}s;



void bfs()

{

	int i;

	s.step = 0;

	priority_queue <node> q;

	q.push(s);

	while(!q.empty())

	{

		node p = q.top();

		q.pop();

		if(p.x == 0 || p.y == 0 || p.x == 1001 || p.y == 1001)

		{

			printf("%d\n",p.step);

			return;

		}

		for(i = 0;i < 4; i++)

		{

			node t;

			t.x = p.x + dir[i][0];

			t.y = p.y + dir[i][1];

			t.step = p.step;

			if(a[t.x][t.y] == -1)

				continue;

			if(a[t.x][t.y])

				t.step++;

			a[t.x][t.y] = -1;

			q.push(t);

		}

			

	}

}

int main()

{

	int n,x,y;

	scanf("%d %d %d",&n,&s.x,&s.y);

	while(n--)

	{

		scanf("%d %d",&x,&y);

		a[x][y] = 1;

	}

	bfs();

	return 0;

}

 

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