题目描述
Problem Statement
You are given a simple connected undirected graph G with N vertices and M edges.
The vertices and edges of G are numbered as vertex $1, vertex 2, \ldots, vertex N$, and edge $1, edge 2, \ldots, edge M,$ respectively, and edge $i (1\leq i\leq M) connects vertices U_i$ and V_i.
You are also given distinct vertices A,B,C on G.
Determine if there is a simple path connecting vertices A and C via vertex B.
What is a simple connected undirected graph?
A graph G is said to be a simple connected undirected graph when G is an undirected graph that is simple and connected.
A graph G is said to be an undirected graph when the edges of G have no direction.
A graph G is simple when G does not contain self-loops or multi-edges.
A graph G is connected when one can travel between all vertices of G via edges.
What is a simple path via vertex Z?
For vertices X and Y on a graph G, a simple path connecting X and Y is a sequence of distinct vertices $(v_1,v_2,\ldots,v_k)$ such that v_1=X, v_k=Y, and for every integer $i satisfying 1\leq i\leq k-1,$ there is an edge on G connecting vertices v_i and v_{i+1}.
$A simple path (v_1,v_2,\ldots,v_k)$ is said to be via vertex Z when there is an $i (2\leq i\leq k-1) satisfying v_i=Z$.
Input
The input is given from Standard Input in the following format:
N M
A B C
U_1 V_1
U_2 V_2
$\vdots$
U_M V_M
Output
If there is a simple path that satisfies the condition in the statement, print Yes; otherwise, print No.
Constraints
- $3 \leq N \leq 2\times 10^5$
- $N-1\leq M\leq\min\left(\frac{N(N-1)}{2},2\times 10^5\right)$
- $1\leq A,B,C\leq N$
- A, B, and C are all distinct.
- $1\leq U_i<V_i\leq N$
- The pairs (U_i,V_i) are all distinct.
- All input values are integers.
Sample Input 1
6 7
1 3 2
1 2
1 5
2 3
2 5
2 6
3 4
4 5
Sample Output 1
Yes
One simple path connecting vertices 1 and 2 via vertex 3 is $1 \to$ $5 \to$ $4 \to$ $3 \to$ 2.
Thus, print Yes.
Sample Input 2
6 6
1 3 2
1 2
2 3
2 5
2 6
3 4
4 5
Sample Output 2
No
No simple path satisfies the condition. Thus, print No.
Sample Input 3
3 2
1 3 2
1 2
2 3
Sample Output 3
No
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分