ZOJ 1857 && POJ 2607 Fire Station【SPFA】

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本文介绍了一种基于最短路径算法的优化方案，通过邻接矩阵和邻接表两种方式实现，针对不同输入数据特点调整算法策略，以提高计算效率。

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//ylwh	2607	Accepted	1356K	1047MS	G++	1520B	2011-08-08 20:22:30【SFPA】
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <algorithm>
using namespace std;
#define N 505
#define MAX 200000000
int main()
{
	int nf, ni, ans, len;
	int staue[N], flag[N], Q[N], d[N], map[N][N];
	int i, j, k, temp, maxs, head, tail, now;
	char s[20];
	while(scanf("%d%d", &nf, &ni) != EOF)
	{
		ans = 1;
		len = MAX;
		memset(map, 0, sizeof(map));
		memset(flag, 0, sizeof(flag));
		for(i=1; i<=nf; i++)
		{
			scanf("%d", &k);
			map[0][k] = 1;
			flag[k]++;
		}
		getchar();
		while(gets(s) && strlen(s) > 1)
		{
			sscanf(s,"%d%d%d", &i, &j, &k);
			map[i][j] = map[j][i] = k;
		}
		for(i=1; i<=ni; i++)
		{
			if( !flag[i])
			{
				for(j=1; j<=ni; j++)
					d[j] = MAX;
				map[0][i] = 1;
				memset(staue, 0, sizeof(staue));
				head = 0;
				tail = 1;
				Q[head] = 0;
				staue[0] = 1;
				d[0] = -1;
				while(head != tail)
				{
					now = Q[head];
					for(j=1; j<=ni; j++)
					{
						if(map[now][j] && d[j] > map[now][j] + d[now])
						{
							if( !staue[j])
							{
								Q[tail++] = j;
								staue[j] = 1;
								tail %= ni + 5;
							}
							d[j] = map[now][j] + d[now];
						}
					}
					staue[now] = 0;
					head = (head + 1) % (ni + 5);
				}
				maxs = 0;
				for(j=1; j<=ni; j++)
				{
					if(d[j] > maxs)
						maxs = d[j];
				}
				if(maxs < len)
				{
					len = maxs;
					ans = i;
				}
				map[0][i] = 0;
			}
		}
		printf("%d\n", ans);
	}
	return 0;
}

继续改写中。。。。。。。

改写后版本：

//2619852 	2011-08-08 20:33:40 	Accepted 	1857 	C 	50 	160 	ylwh!
//9111412	ylwh	2607	Accepted	1364K	47MS	G++	1977B	2011-08-08 20:34:31
#include <stdio.h>
#include <string.h>
#define N 505
#define MAX 200000000
int main()
{
	int nf, ni, ans, len;
	int staue[N], flag[N], Q[N], d[N], map[N][N];
	int i, j, k, temp[N], maxs, head, tail, now;
	char s[20];
	while(scanf("%d%d", &nf, &ni) != EOF)
	{
		ans = 1;
		len = MAX;
		memset(map, 0, sizeof(map));
		memset(flag, 0, sizeof(flag));
		for(i=1; i<=nf; i++)
		{
			scanf("%d", &k);
			map[0][k] = 1;
			flag[k]++;
		}
		getchar();
		while(gets(s) && strlen(s) > 1)
		{
			sscanf(s,"%d%d%d", &i, &j, &k);
			map[i][j] = map[j][i] = k;
		}
		for(j=1; j<=ni; j++)
			temp[j] = MAX;
		memset(staue, 0, sizeof(staue));
		head = 0;
		tail = 1;
		Q[head] = 0;
		staue[0] = 1;
		temp[0] = -1;
		while(head != tail)
		{
			now = Q[head];
			for(j=1; j<=ni; j++)
			{
				if(map[now][j] && temp[j] > map[now][j] + temp[now])
				{
					if( !staue[j])
					{
						Q[tail++] = j;
						staue[j] = 1;
						tail %= ni + 5;
					}
					temp[j] = map[now][j] + temp[now];
				}
			}
			staue[now] = 0;
			head = (head + 1) % (ni + 5);
		}
		maxs = 0;
		for(i=1; i<=ni; i++)
		{
			if( !flag[i])
			{
				for(j=0; j<=ni; j++)
					d[j] = temp[j];
				map[0][i] = 1;
				memset(staue, 0, sizeof(staue));
				head = 0;
				tail = 1;
				Q[head] = 0;
				staue[0] = 1;
				while(head != tail)
				{
					now = Q[head];
					for(j=1; j<=ni; j++)
					{
						if(map[now][j] && d[j] > map[now][j] + d[now])
						{
							if( !staue[j])
							{
								Q[tail++] = j;
								staue[j] = 1;
								tail %= ni + 5;
							}
							d[j] = map[now][j] + d[now];
						}
					}
					staue[now] = 0;
					head = (head + 1) % (ni + 5);
				}
				maxs = 0;
				for(j=1; j<=ni; j++)
				{
					if(d[j] > maxs)
						maxs = d[j];
				}
				if(maxs < len)
				{
					len = maxs;
					ans = i;
				}
				map[0][i] = 0;
			}
		}
		printf("%d\n", ans);
	}
	return 0;
}

继续改写中（邻接表， T_T, 对于我很难写啊。。。。。。

//2620886 	2011-08-09 21:43:57 	Accepted 	1857 	C 	0 	276 	ylwh!
#include <stdio.h>
#include <string.h>
#define N 505
#define MAX 200000000
struct edge
{
	int num, len;
	struct edge * next;
}e[10005];
int main()
{
	int nf, ni, ans, len;
	int staue[N], flag[N], d[N], Q[N+5];
	int i, j, k, temp[N], maxs, now, head, tail;
	struct edge * next;
	char s[20];
	while(fscanf(stdin, "%d%d", &nf, &ni) != EOF)
	{
		ans = 1;
		len = MAX;
		for(j=1; j<=ni; j++)
			temp[j] = MAX;
		memset(staue, 0, sizeof(staue));
		memset(flag, 0, sizeof(flag));
		for(i=1; i<=ni; i++)
		{
			e[i].num = i;
			e[i].next = NULL;
		}
		head = -1;
		for(i=1; i<=nf; i++)
		{
			fscanf(stdin, "%d", &k);
			flag[k]++;
			temp[k] = 0;
			staue[k] = 1;
			Q[++head] = k;
		}
		tail = head + 1;
		head = ni;
		getchar();
		while(fgets(s, 20, stdin) && strlen(s) > 1)
		{
			sscanf(s,"%d%d%d", &i, &j, &k);
			e[++head].num = j;
			e[head].len = k;
			e[head].next = e[i].next;
			e[i].next = e + head;

			e[++head].num = i;
			e[head].len = k;
			e[head].next = e[j].next;
			e[j].next = e + head;
		}
		head = 0;
		while(head != tail)
		{
			now = Q[head];
			next = e[now].next;
			while(next != NULL)
			{
				if(temp[ next->num ] > temp[now] + next->len)
				{
					temp[ next->num ] = temp[now] + next->len;
					if( !staue[next->num])
					{
						Q[tail++] = next->num;
						staue[ next->num] = 1;
						tail %= ni + 5;
					}
				}
				next = next->next;
			}
			head++;
			head %= ni + 5;
		}
		for(i=1; i<=ni; i++)
		{
			if( !flag[i] )
			{
				for(j=1; j<=ni; j++)
					d[j] = temp[j];
				memset(staue, 0, sizeof(staue));
				tail = 1;
				head = 0;
				Q[head] = i;
				staue[i] = 1;
				d[i] = 0;
				while(head != tail)
				{
					now = Q[head];
					next = e[now].next;
					while(next != NULL)
					{
						if(d[ next->num ] > d[now] + next->len)
						{
							d[ next->num ] = d[now] + next->len;
							if( !staue[next->num])
							{
								Q[tail++] = next->num;
								staue[ next->num] = 1;
								tail %= ni + 5;
							}
						}
						next = next->next;
					}
					head++;
					head %= ni + 5;
				}
				maxs = 0;
				for(j=1; j<=ni; j++)
					if(d[j] > maxs)
						maxs = d[j];
				if(maxs < len)
				{
					len = maxs;
					ans = i;
				}
			}
		}
		printf("%d\n", ans);
	}
	return 0;
}