典型的bfs最短路搜索
框架
void bfs()
{
q.push(起点);
while(队列不空)
{
auto t = 队首元素;
for(所有相邻节点)
{
如果可以扩展,就扩展,入队;
}
}
}
代码
//bfs
#include<bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int n, m;
int h[N], e[N], ne[N], idx = 0;
void add(int a, int b)
{
e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}
int d[N];
int bfs()
{
queue<int> q;
q.push(1);
memset(d, -1, sizeof d);
d[1] = 0;
while(q.size())
{
auto t = q.front();q.pop();
for(int i = h[t]; i != -1; i = ne[i])
{
int j = e[i];
if(d[j] == -1)
{
d[j] = d[t] + 1;
q.push(j);
}
}
}
return d[n];
}
int main()
{
cin >> n >> m;
memset(h, -1, sizeof h);
for(int i = 0; i < m ;i++)
{
int a, b;
cin >> a >> b;
add(a, b);
}
cout << bfs() << endl;
return 0;
}