RQNOJ 34 紧急援救 解题报告

　　SPFA，直接搜索就行，代码如下：

#include <stdio.h>
#include <stdlib.h>
#define Q_MAX 100000
char map[1000][1000];
int dis[1000][1000];
struct node{
	int x, y;
}queue[Q_MAX];
int head, rear;
int used[1000][1000];

void enqueue(int a, int b)
{
	if(used[a][b]){
		return;
	}
	used[a][b] = 1;
	queue[rear].x = a;
	queue[rear].y = b;
	rear = (rear + 1) % Q_MAX;
}

void exqueue(int *a, int *b)
{
	*a = queue[head].x;
	*b = queue[head].y;
	used[*a][*b] = 0;
	head = (head + 1) % Q_MAX;
}

int main(int argc, char **argv)
{
	int i, j;
	int a, b;
	int x, y;
	int n;
	scanf("%d\n", &n);
	for(i = 0; i < n; i++){
		for(j = 0; j < n; j++){
			scanf("%c", &map[i][j]);
			dis[i][j] = 0xFFFFFFF;
			map[i][j] -= '0';
		}
		scanf("\n");
	}
	scanf("%d%d", &a, &b);
	dis[a - 1][b - 1] = 0;
	enqueue(a - 1, b - 1);
	scanf("%d%d", &a, &b);
	a--, b--;
	while(head != rear){
		exqueue(&x, &y);
#define deal(a, b) if(((a) >= 0 && (a) < n && (b) >= 0 && b < n) && (!map[a][b]) && dis[a][b] > dis[x][y] + 1){\
	dis[a][b] = dis[x][y] + 1;\
	enqueue((a), (b));\
}
		deal(x + 1, y);
		deal(x - 1, y);
		deal(x, y - 1);
		deal(x, y + 1);
	}
	printf("%d\n", dis[a][b]);
	return 0;
}