NYOJ592 spiral grid 【BFS】

标签：nyoj592

描述

Xiaod has recently discovered the grid named "spiral grid".
Construct the grid like the following figure. (The grid is actually infinite. The figure is only a small part of it.)


Considering traveling in it, you are free to any cell containing a composite number or 1, but traveling to any cell containing a prime number is disallowed. In addition, traveling from a prime number is disallowed, either. You can travel up, down, left or right, but not diagonally. Write a program to find the length of the shortest path between pairs of nonprime numbers, or report it‘s impossible.

输入

Each test case is described by a line of input containing two nonprime integer 1 <=x, y<=10,000.

输出

For each test case, display its case number followed by the length of the shortest path or "impossible" (without quotes) in one line.

样例输入

1 4
9 32
10 12

样例输出

Case 1: 1
Case 2: 7
Case 3: impossible

构图的时候要格外细心。

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <queue>
#define abs(a) (a) > 0 ? (a) : -(a)
using std::queue;

int map[102][102], vis[102][102], prime[10002] = {1, 1};
int x, y, mov[][2] = {0, 1, 0, -1, 1, 0, -1, 0};
struct Node{
	int x, y, steps;
};
queue<Node> Q;

void preprocess(){
	//画图的时候要细心
	int count = 10000, x = 2, y = 2;
	for(int i = 1; i <= 100; ++i)
		map[1][i] = count--;
	for(int i = 2; i <= 100; ++i)
		map[i][100] = count--;
	for(int i = 99; i > 0; --i)
		map[100][i] = count--;
	for(int i = 99; i > 1; --i)
		map[i][1] = count--;
	map[2][2] = count--;
	while(count > 0){
		while(!map[x][y+1]) map[x][++y] = count--;
		while(!map[x+1][y]) map[++x][y] = count--;
		while(!map[x][y-1]) map[x][--y] = count--;
		while(!map[x-1][y]) map[--x][y] = count--;
	}	
}

Node getX(){
	Node t = {0};
	for(int i = 1; i < 101; ++i)
		for(int j = 1; j < 101; ++j){
			if(map[i][j] == x){
				t.x = i; t.y = j;
				return t;
			}
		}
}

void getPrime(){
	for(int i = 2; i <= 100; ++i){
		if(prime[i]) continue;
		for(int j = i * i; j <= 10000; j += i)
			prime[j] = 1;
	}
}

int check(Node t){
	if(t.x < 1 || t.y < 1 || t.x > 100 || t.y > 100)
		return 0;
	if(vis[t.x][t.y] || !prime[map[t.x][t.y]])
		return 0;
	return 1;
}

void BFS(){
	Node temp, now;
	while(!Q.empty()) Q.pop();
	now = getX();
	if(x == y){
		printf("0\n"); return;
	}
	Q.push(now);
	
	while(!Q.empty()){
		now = Q.front();
		Q.pop();
		
		for(int i = 0; i < 4; ++i){
			temp = now;
			temp.x += mov[i][0];
			temp.y += mov[i][1];
			++temp.steps;
			
			if(check(temp)){
				if(map[temp.x][temp.y] == y){
					printf("%d\n", temp.steps);
					return;
				}
				vis[temp.x][temp.y] = 1;
				Q.push(temp);
			}
		}
	}
	printf("impossible\n");
}

int main(){
	getPrime();
	preprocess();
	int times = 1;
	while(scanf("%d%d", &x, &y) == 2){
		printf("Case %d: ", times++);
		memset(vis, 0, sizeof(vis));
		BFS();
	}
	return 0;
}

NYOJ592 spiral grid 【BFS】,布布扣,bubuko.com

NYOJ592 spiral grid 【BFS】

标签：nyoj592

原文地址：http://blog.csdn.net/chang_mu/article/details/32335611