hdu 1595 find the longest of the shortest(dijkstra)

#include <stdio.h>
#include <string.h>
#define INF 99999999
int map[1001][1001];
int vis[1001],dis[1001],link[1001];
int n,m;

int max(int a, int b)
{
return a > b ? a : b;
}

void dijkstra(int s, int flag)
{
int i,j,min,pos;
memset(vis,0,sizeof(vis));
for(i = 1; i <= n; ++i)
dis[i] = INF;
dis[s] = 0;
for(i = 1; i < n; ++i)
{
min = INF;
for(j = 1; j <= n; ++j)
{
if(dis[j] < min && !vis[j])
min = dis[pos = j];
}
vis[pos] = 1;
for(j = 1; j <= n; ++j)
if(dis[pos] + map[pos][j] < dis[j])
{
dis[j] = dis[pos] + map[pos][j];
if(flag)//只记录最短那条路的父节点
link[j] = pos;
}
}
}

int main()
{
int i,j,x,y,w;
while(scanf("%d %d",&n,&m) != EOF)
{
for(i = 1; i <= n; ++i)
{
for(j = 1; j <= n; ++j)
map[i][j] = INF;
map[i][i] = 0;
}
while(m--)
{
scanf("%d%d%d",&x,&y,&w);
if(w < map[x][y])
map[x][y] = map[y][x] = w;
}
memset(link,0,sizeof(link));
dijkstra(1,1);
int ans = dis
;
for(i = n; i != 1; i = link[i])
{
int tem = map[i][link[i]];//当前最短路到父节点的距离先存起来
map[i][link[i]] = map[link[i]][i] = INF;
dijkstra(1,0);
ans = max(ans,dis
);
map[i][link[i]] = map[link[i]][i] = tem;//恢复当前的最短路
}
printf("%d\n",ans);
}
return 0;
}