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@@ -0,0 +1,61 @@
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+#include <cstdio>
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+#include <cstring>
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+#include <vector>
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+#include <queue>
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+
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+using std::vector; using std::queue;
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+
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+const int N = 100000;
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+const int M = 200000;
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+
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+struct node {
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+ int x;
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+ int y;
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+ node(int x, int y) : x(x), y(y) {}
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+};
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+
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+vector<node> g[N + 1];
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+
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+int dis[N + 1];
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+
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+int main() {
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+ int n, m;
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+ scanf("%d %d", &n, &m);
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+ for (int i = 0, p, q, c; i < m; i++) {
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+ scanf("%d %d %d", &p, &q, &c);
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+ if (p == q) continue;
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+ g[p].push_back(node(q, c));
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+ g[q].push_back(node(p, c));
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+ }
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+ memset(dis, -1, sizeof(dis));
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+ queue<int> q;
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+ q.push(n);
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+ dis[n] = 0;
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+ int d = 0, size = q.size();
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+ while (size != 0) {
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+ int cur = q.front();
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+ q.pop();
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+ if (cur == 1) break;
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+ size--;
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+ for (node i : g[cur]) {
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+ if (dis[i.x] == -1) {
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+ dis[i.x] = d + 1;
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+ q.push(i.x);
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+ }
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+ }
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+ if (size == 0) {
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+ size = q.size();
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+ d++;
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+ }
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+ }
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+ printf("%d\n", d);
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+ q = queue<int>();
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+ q.push(1);
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+ while (!q.empty()) {
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+ int cur = q.front();
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+ q.pop();
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+ if (cur == n) break;
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+
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+ }
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+ return 0;
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+}
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