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# Edexcel D1 - 17th June, 2016 [Exam discussion] watch

1. (Original post by pecora)
Right, my attempt.

a) you make comparisons between first and second number on the list and the one which is bigger you "push" to the left and compare the remaining number with the next one. Repeat till the end of the pass and do other passes until you cannot do any more swaps - that's when the list is in order.

b) i) last one — basically what you are doing is "pushing" all the smaller bits to the end
ii) that'll happen when the list is in complete mess, i. e. you need to resort 1, 2, 3, 4 into descending. you will need 3 passes. So n-1 passes.
Wrong, it would be the smallest number of course.
2. Help with Past paper Q!!! The last Q in that page, why's Using prims algorithm wrong??
3. (Original post by Yua)
Wrong, it would be the smallest number of course.
It asks which number, so I guess both answers should be correct — why wouldn't they give me a mark if I said the last one in that pass?
4. (Original post by pecora)
My gut senses are saying we'll find a trace table in the exam tomorrow.
Yikes- what's a trace table :P
5. (Original post by The Curious One)
Help with Past paper Q!!! The last Q in that page, why's Using prims algorithm wrong??
I think you need to use kruskals because that looks at edges like the 2 given rather than nodes
6. (Original post by The Curious One)
Help with Past paper Q!!! The last Q in that page, why's Using prims algorithm wrong??
Because in Prims you grow a connected tree whilst in kruskal you grow a non connected tree which is good because you already have two edges
7. predictions for tomorrow??
8. (Original post by The Curious One)
Help with Past paper Q!!! The last Q in that page, why's Using prims algorithm wrong??
I don't even know how to use Prim's on this, it's impossible because Prim's must start at a vertex rather than an edge — and here you are given two edges which absolutely must be in the tree — how would you ensure that those specific edges appear on Prim's?

Use Kruskal's (1), start the algorithm with those two edges (2) and then continue like you would normally — selecting the smallest ones that don't form a cycle till the tree is connected. Full marks.
9. (Original post by Romanianduchess)
Because in Prims you grow a connected tree whilst in kruskal you grow a non connected tree which is good because you already have two edges
Lovely
10. (Original post by willroberts98)
predictions for tomorrow??
I predict a D1 exam <3
11. Jack and Daniel are up late studying for D1.
Jack completes a bin packing problem and notes that the total wasted space is less the the size of a single bin.
Daniel claims that the solution is optimal, but Jack is skeptical. How should Daniel argue his case?
12. Ahhh right forgot about that, thanks guys!!!
Also does it matter which order we use in placing non-critical activities in a Gantt/Cascade chart? If so, then what sort of order?
13. (Original post by thelegend99)
Yikes- what's a trace table :P
Trace table? Whaaaat??

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14. (Original post by pecora)
I don't even know how to use Prim's on this, it's impossible because Prim's must start at a vertex rather than an edge — and here you are given two edges which absolutely must be in the tree — how would you ensure that those specific edges appear on Prim's

Use Kruskal's (1), start the algorithm with those two edges (2) and then continue like you would normally — selecting the smallest ones that don't form a cycle till the tree is connected. Full marks.

I would've started at probably one of those 4 nodes (say node A) and grown the tree from there
15. I swear its not on the syllabus

(Original post by Themathgeek)
Trace table? Whaaaat??

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16. (Original post by thelegend99)
I swear its not on the syllabus
Ikr
17. (Original post by The Curious One)
I would've started at probably one of those 4 nodes (say node A) and grown the tree from there
That's not Prim's algorithm then, that's Booleshite's algorithm Prim's has to start at one vertex and then go from there. Not two.
18. What's the paper with the handshaking lemma proof model answer on it?
19. (Original post by theoriginalrpr)
does anyone have a link to the jan 2016 paper for d1? thanks
(Original post by Pablo Picasso)
Looking for it aswell
This guy has everything:
https://56leomessiphotoshop.blogspot...materials.html
20. (Original post by The Curious One)
Ahhh right forgot about that, thanks guys!!!
Also does it matter which order we use in placing non-critical activities in a Gantt/Cascade chart? If so, then what sort of order?
The Mark Schemes normally order the non-criticals alphabetically so that's what I would do

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