C#•10mo ago

✅ I don't understand what I did wrong(list)

a list is a circle if its last node points at a previous node. I tried writing a function that can tell whether a given list is a circle, it works except for the last 3 check ups where it loops forever. I provided pics of my code and the running code. *ListFromString points the last node of a given list of int at the first one) *I only had problems with the code inside the for loop

6 Replies

𝓭𝓾𝓼𝓴𝔂 🐸OP•10mo ago

I believe the problem must be caused by the circle part of the list repeating itself over and over but curr1 and curr2 should meet and I checked it on paper and it seemed to work so I'm not sure what the problem is

Kouhai•10mo ago

a list is a circle if its last node points at a previous node. Do you mean if it's last node points at the first node? Or just if it points at any previous node?

𝓭𝓾𝓼𝓴𝔂 🐸OP•10mo ago

any previous one in the for loop it'd be 1->0 -> 0 ->... and it's still considered a circle

Kouhai•10mo ago

You can use Floyd's cycle-finding algorithm, it would be something like

var n1 = node1;
var n2 = node1;
while(n1 != null && n1.Next != null)
{
  n2 = n2.Next;
  n1 = n1.Next.Next;
  if(n1 == n2)
  {
    return true;
  }
}
return false;

var n1 = node1;
var n2 = node1;
while(n1 != null && n1.Next != null)
{
  n2 = n2.Next;
  n1 = n1.Next.Next;
  if(n1 == n2)
  {
    return true;
  }
}
return false;

𝓭𝓾𝓼𝓴𝔂 🐸OP•10mo ago

Kouhai•10mo ago

The idea behind the algorithim is that n1 moves faster So for example 0 -> 1 -> 3 -> 1 ^ n1 n2 1 iteration 0 -> 1 -> 3 -> 1 ^ ^ n2 n1 2 iteration 0 -> 1 -> 3 -> 1 ^ ^
n1 n2
3 iteration 0 -> 1 -> 3 -> 1 ^ ^ n1 n2 4 iteration 0 -> 1 -> 3 -> 1 ^ n1 n2 Means it's a full cycle

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✅ I don't understand what I did wrong(list)