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| #include <iostream>
#include <cstdio>
#include <climits>
#include <queue>
#include <stack>
#define inf INT_MAX
using namespace std;
const int N = 2e5 + 10, M = 2e6 + 10;
bool vis[N];
int n, m, cnt, d[N];
int idx = -1, hd[N], nxt[M], edg[M], wt[N];
int stmp, id[N], dfn[N], low[N], num[N];
stack <int> stk;
void tarjan(int x)
{
dfn[x] = low[x] = ++stmp;
stk.push(x);
vis[x] = true;
for (int i = hd[x]; ~i; i = nxt[i])
if (!dfn[edg[i]])
{
tarjan(edg[i]);
low[x] = min(low[x], low[edg[i]]);
}
else if (vis[edg[i]])
low[x] = min(low[x], dfn[edg[i]]);
if (dfn[x] == low[x])
{
int y;
cnt++;
do
{
y = stk.top();
stk.pop();
vis[y] = false;
id[y] = cnt;
num[cnt]++;
} while (y != x);
}
}
void spfa()
{
for (int i = 1; i <= n; i++)
d[i] = inf;
for (int i = 1; i <= n; i++)
vis[i] = false;
d[1] = 0;
queue <int> q;
q.push(1);
vis[1] = true;
while (!q.empty())
{
int t = q.front();
q.pop();
vis[t] = false;
for (int i = hd[t]; ~i; i = nxt[i])
if (d[t] + wt[i] < d[edg[i]])
{
d[edg[i]] = d[t] + wt[i];
if (!vis[edg[i]])
{
q.push(edg[i]);
vis[edg[i]] = true;
}
}
}
}
void add(int a, int b, int c)
{
nxt[++idx] = hd[a];
hd[a] = idx;
edg[idx] = b;
wt[idx] = c;
}
int main()
{
cin >> n >> m;
for (int i = 1; i <= n; i++)
hd[i] = -1;
for (int i = 1, a, b, c; i <= m; i++)
{
cin >> a >> b >> c;
add(a, b, c);
}
for (int i = 1; i <= n; i++)
if (!dfn[i])
tarjan(i);
for (int i = 1; i <= n; i++)
for (int j = hd[i]; ~j; j = nxt[j])
if (id[i] == id[edg[j]])
wt[j] = 0;
spfa();
cout << d[n];
return 0;
}
|