This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include<cstdio>
#include<vector>
#include<queue>
using namespace std;
const int INF = 987654321;
int n, m;
vector<vector<int>> edge;
int dijkstra() {
vector<int> dist(n, -1);
vector<bool> discovered(n);
discovered[0] = 1;
dist[0] = 0;
queue<int> q;
q.push(0);
while(!q.empty()) {
int here = q.front();
q.pop();
for (int i=0; i<edge[here].size(); ++i) {
int there = edge[here][i];
if (discovered[there]) continue;
dist[there] = dist[here] + 1;
discovered[there] = 1;
q.push(there);
}
}
return dist[n-1];
}
int main() {
scanf("%d%d", &n, &m);
edge = vector<vector<int>>(n);
for (int i=0; i<m; ++i) {
int x, y;
scanf("%d%d", &x, &y);
--x; --y;
edge[x].push_back(y);
}
printf("%d\n", dijkstra());
return 0;
}
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