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PORed-Black Tree Insertion Fixup Error
 

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    <p>I have a homework problem about inserting into red-black trees in c#. I wrote the code below and the program works without any problems for adding first 3 numbers. When I try to add the 4th number, I get a NullReferenceException. I'm trying to solve the error for 2 days but I can't figure it out.</p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Algoritmalar3b { class rbtNode { public int? key; public char? color; public rbtNode left, right, p; public rbtNode(int? key, char? color, rbtNode left, rbtNode right, rbtNode p) { this.key = key; this.color = color; this.left = left; this.right = right; this.p = p; } } class Program { static rbtNode Tnil = new rbtNode(null, 'B', null, null, null); static void Main(string[] args) { rbtNode root = new rbtNode(null, 'B', Tnil, Tnil, null); RB_Insert(root, 7); RB_Insert(root, 3); RB_Insert(root, 89); RB_Insert(root, 4); RB_Insert(root, 9); RB_Insert(root, 15); RB_Insert(root, 35); RB_Insert(root, 8); RB_Insert(root, 24); preOrderWalk(root); } static void RB_Insert(rbtNode T, int? deger) { rbtNode z = new rbtNode(deger, null, Tnil, Tnil, null); if (T.key == null) T.key = deger; else { rbtNode y = new rbtNode(null, null, Tnil, Tnil, null); y = Tnil; rbtNode x = new rbtNode(null, null, Tnil, Tnil, null); x = T; while (x != Tnil) { y = x; if (z.key &lt; x.key) x = x.left; else x = x.right; } z.p = y; if (y == Tnil) T = z; else if (z.key &lt; y.key) y.left = z; else y.right = z; z.left = Tnil; z.right = Tnil; z.color = 'R'; RB_Insert_Fixup(T, z); } } static void RB_Insert_Fixup(rbtNode T, rbtNode z) { rbtNode y = new rbtNode(null, null, Tnil, Tnil, null); while (z.p.color == 'R') { if (z.p == z.p.p.left) { y = z.p.p.right; if (y.color == 'R') { z.p.color = 'B'; y.color = 'B'; z.p.p.color = 'R'; z = z.p.p; } else if (z == z.p.right) { z = z.p; Left_Rotate(T, z); z.p.color = 'B'; z.p.p.color = 'R'; Right_Rotate(T, z.p.p); } } else { y = z.p.p.left; if (y.color == 'R') { z.p.color = 'B'; y.color = 'B'; z.p.p.color = 'R'; z = z.p.p; } else if (z == z.p.left) { z = z.p; Left_Rotate(T, z); z.p.color = 'B'; z.p.p.color = 'R'; Right_Rotate(T, z.p.p); } } } T.color = 'B'; } static void Left_Rotate(rbtNode T, rbtNode x) { rbtNode y = new rbtNode(null, null, Tnil, Tnil, null); y = x.right; x.right = y.left; if (y.left != Tnil) y.left.p = x; y.p = x.p; if (x.p == Tnil) T = y; else if (x == x.p.left) x.p.left = y; else x.p.right = y; y.left = x; x.p = y; } static void Right_Rotate(rbtNode T, rbtNode x) { rbtNode y = new rbtNode(null, null, Tnil, Tnil, null); y = x.left; x.left = y.right; if (y.right != null) y.right.p = x; y.p = x.p; if (x.p == null) T = y; else if (x == x.p.right) x.p.right = y; else x.p.left = y; y.right = x; x.p = y; } static void preOrderWalk(rbtNode T) { if (T.color == 'B') Console.WriteLine("-{0}", T.key); else Console.WriteLine("{0}", T.key); if (T.left != null) preOrderWalk(T.left); if (T.right != null) preOrderWalk(T.right); } } </code></pre> <p>}</p>
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    1. USChris Kooken
    1. USAhmetEmre90
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    1. This table or related slice is empty.
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      1. VTDownMod
    2. VO
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    1. COStep through a minimal tree exhibiting the behavior with a debugger and a piece of paper (draw out what is happening and what should be happening). Or, at the very least, indicate the line the exception is being generated on.
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    2. COWelcome to StackExchange! Your question is probably better suited for http://codereview.stackexchange.com/ :)
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      1. USblubb
    3. CO@pst i did everything you said 4-5 times, but i couldn't find the solve
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      1. USAhmetEmre90
 

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