And query set exercises --- poj 1182 food chain

Typical query questions.

It mainly maintains the relationship between nodes.

First, let's look at the path compression section:

[Cpp]
Int find (int x)
{
If (fa [x] = x) return x;
Int t = fa [x];
Fa [x] = find (fa [x]);
R [x] = (r [x] + r [t]) % 3;
Return fa [x];
}
Save the original parent node.
Let's see how to merge:

[Cpp]
Fx = find (x); fy = find (y );
If (fx! = Fy)
{
Fa [fy] = fx;
C --;
R [fy] = (r [x]-r [y]-c + 6) % 3;
}
You can find the rule by enumerating some situations. As for why to add 6, it is to ensure that it is positive (because of-c, it cannot only add 3)
Finally, determine whether it is true:

[Cpp]
If (c = 1) ans + = r [x]! = R [y];
Else ans + = (r [x]-r [y] + 3) % 3! = 1;
This solves the problem.

 

 

Author: ascii991