2023-8-28 图中点的层次(树与图的广度优先遍历)

题目链接：图中点的层次

#include <iostream>
#include <cstring>
#include <algorithm>using namespace std;const int N = 100010;int h[N], e[N], ne[N], idx;
int n, m;
int q[N], d[N];void add(int a, int b)
{e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}int bfs()
{int hh = 0, tt = 0;q[0] = 1;memset(d, -1,sizeof d);d[1] = 0;while(hh <= tt){int t = q[hh++];for(int i = h[t]; i != -1; i = ne[i]){int j = e[i];if(d[j] == -1){d[j] = d[t] + 1;q[++tt] = j;}}}return d[n];
}int main()
{cin >> n >> m;memset(h, -1, sizeof h);while(m--){int a, b;cin >> a >> b;add(a, b);}cout << bfs() <<endl;return 0; 
}