6978.Fixed Length Walk Queries

Time Limit: 1s Memory Limit: 512MB

You are given an undirected graph with $n$ nodes and $m$ edges. The graph is simple and connected.

You start at a specific node, and on each turn
you must move through an edge to another node.

Your task is to answer $q$ queries of the form: "is it possible to start at node $a$ and end up on node $b$ after exactly $x$ turns?"

Input Format(From the terminal/stdin)

The first line contains three integers $n$ , $m$ and $q$ :
the number of nodes, edges and queries. The nodes are numbered $1,2,\dots,n$ .

After this, there are $m$ lines which describe the edges. Each line contains two integers $a$ and $b$ : there is an edge between nodes $a$ and $b$ .

Finally, there are $q$ lines, each describing a query.
Each line contains three integers $a$ , $b$ and $x$ .

  • $2 \le n \le 2500$
  • $1 \le m \le 5000$
  • $1 \le q \le 10^5$
  • $0 \le x \le 10^9$

Output Format(To the terminal/stdout)

For each query, print the answer ( YES or NO ) on its own line.

Sample Input

Copy
4 5 6
1 2
2 3
1 3
2 4
3 4
1 2 2
1 4 1
1 4 5
2 2 1
2 2 2
3 4 8
 · · \n
 · \n
 · \n
 · \n
 · \n
 · \n
 · · \n
 · · \n
 · · \n
 · · \n
 · · \n
 · · \n

Sample Output

Copy
YES
NO
YES
NO
YES
YES
   \n
  \n
   \n
  \n
   \n
   \n
  • In query 1, a possible route is $1 \rightarrow 3 \rightarrow 2$ .
  • In query 3, a possible route is $1 \rightarrow 3 \rightarrow 2 \rightarrow 1 \rightarrow 3 \rightarrow 4$ .
  • In query 6, a possible route is $3 \rightarrow 4 \rightarrow 2 \rightarrow 3 \rightarrow 4 \rightarrow 2 \rightarrow 1 \rightarrow 3 \rightarrow 4$ .
Source: CSES, Advanced Graph Problems, 3357

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