【洛谷 1186】 玛丽卡

又是开错了数组……要记住。

#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pii pair<int,int>
#define mp(a,b) make_pair(a,b)
const int maxn = 1010;
const int maxm = 1100010+100000;
const int inf = 0x7fffffff/3;
int _first[maxn], _next[maxm], _to[maxm], _dis[maxm], cnt, dis[maxn];
int n, m;
priority_queue <pii, vector<pii>, greater<pii> > q1;
bool vis[maxn], used[maxm];
pii pre[maxn];
void add(int a, int b, int c){
_next[++cnt] = _first[a];
_first[a] = cnt;
_dis[cnt] = c;
_to[cnt] = b;
}
void dij1(){
while(!q1.empty()) q1.pop();
for(int i = 1; i <= n; i ++) dis[i] = inf, vis[i] = 0;
dis
= 0;
q1.push(mp(dis
, n));
while(!q1.empty()){
pii t = q1.top();
q1.pop();
if(vis[t.se]) continue;
vis[t.se] = true;
if(vis[1]) return;
for(int i = _first[t.se]; i; i = _next[i]){
if(!vis[_to[i]] && dis[_to[i]] > dis[t.se] + _dis[i]){
dis[_to[i]] = dis[t.se] + _dis[i];
pre[_to[i]] = mp(t.se, i);
q1.push(mp(dis[_to[i]], _to[i]));
}
}
}
}
int dij2(){
while(!q1.empty()) q1.pop();
for(int i = 1; i <= n; i ++) dis[i] = inf, vis[i] = 0;
dis
= 0;
q1.push(mp(dis
, n));
while(!q1.empty()){
pii t = q1.top();
q1.pop();
if(vis[t.se]) continue;
vis[t.se] = true;
if(vis[1] == 1) return dis[1];
for(int i = _first[t.se]; i; i = _next[i]){
if(!used[i] && !vis[_to[i]] && dis[_to[i]] > dis[t.se] + _dis[i]){
dis[_to[i]] = dis[t.se] + _dis[i];
q1.push(mp(dis[_to[i]], _to[i]));
}
}
}
}
int main(){
scanf("%d%d", &n, &m);
for(int i = 1; i <= m; i ++){
int a, b, c;
scanf("%d%d%d", &a, &b, &c);
add(a, b, c);
add(b, a, c);
}
dij1();
int ans = 0;
for(int i = 1; i != n; i = pre[i].fi){
used[pre[i].se] = 1;
ans = max(ans, dij2());
used[pre[i].se] = 0;
}
printf("%d", ans);
return 0;
}