题目描述
Problem Statement
A balancing network is an abstract device built up of N wires, thought of as running from left to right,
and M balancers that connect pairs of wires. The wires are numbered from 1 to N from top to bottom,
and the balancers are numbered from 1 to M from left to right.
Balancer i connects wires x_i and y_i (x_i < y_i).
Each balancer must be in one of two states: up or down.
Consider a token that starts moving to the right along some wire at a point to the left of all balancers.
During the process, the token passes through each balancer exactly once.
Whenever the token encounters balancer i, the following happens:
- If the token is moving along wire x_i and balancer i is in the down state, the token moves down to wire y_i and continues moving to the right.
- If the token is moving along wire y_i and balancer i is in the up state, the token moves up to wire x_i and continues moving to the right.
- Otherwise, the token doesn't change the wire it's moving along.
Let a state of the balancing network be a string of length M, describing the states of all balancers.
The i-th character is ^ if balancer i is in the up state, and v if balancer i is in the down state.
A state of the balancing network is called uniforming if a wire w exists such that, regardless of the starting wire,
the token will always end up at wire w and run to infinity along it. Any other state is called non-uniforming.
You are given an integer $T (1 \le T \le 2).$ Answer the following question:
- If T = 1, find any uniforming state of the network or determine that it doesn't exist.
- If T = 2, find any non-uniforming state of the network or determine that it doesn't exist.
Note that if you answer just one kind of questions correctly, you can get partial score.
Input
Input is given from Standard Input in the following format:
N M T
x_1 y_1
x_2 y_2
:
x_M y_M
Output
Print any uniforming state of the given network if T = 1, or any non-uniforming state if T = 2. If the required state doesn't exist, output -1.
Constraints
- $2 \leq N \leq 50000$
- $1 \leq M \leq 100000$
- $1 \leq T \leq 2$
- $1 \leq x_i < y_i \leq N$
- All input values are integers.
Sample Input 1
4 5 1
1 3
2 4
1 2
3 4
2 3
Sample Output 1
^^^^^
This state is uniforming: regardless of the starting wire, the token ends up at wire 1.
Sample Input 2
4 5 2
1 3
2 4
1 2
3 4
2 3
Sample Output 2
v^^^^
This state is non-uniforming: depending on the starting wire, the token might end up at wire 1 or wire 2.
Sample Input 3
3 1 1
1 2
Sample Output 3
-1
A uniforming state doesn't exist.
Sample Input 4
2 1 2
1 2
Sample Output 4
-1
A non-uniforming state doesn't exist.
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分