D1 January 2010 Q3
3.

[The total weight of the network is 167]
Figure 3 represents a network of paths. The number on each arc gives the time, in minutes, to travel along that path.
(a) Use Dijkstra’s algorithm to find the quickest route from A to H. State your quickest route and the time taken. (5)
Kevin must walk along each path at least once and return to his starting point.
(b) Use an appropriate algorithm to find the time of Kevin’s quickest possible route, starting and finishing at A. You should make your method and working clear. (5)
| Scheme | Marks |
|---|---|
![]() | |
| Clear method to include at least 1 update (look at E, F, G or H) | M1 |
| BCDE correct | A1 |
| FGH correct | A1ft |
| Route ADEGH | A1 |
| Total time 36 Minutes | A1ft |
| (5) |
| Scheme | Marks |
|---|---|
| Odd nodes are A, B, C, H | M1 |
| AB + CH = 15 + 25 = 40 | A1 |
| AC + BH = 19 + 22 = 41 | A1 |
| AH + BC = 36 + 22 = 58 | A1 |
| (40 is the shortest, repeating AB and CF + FG + GH) | |
| Must be choosing from at least two pairings for this last mark Shortest time = 167 + 40 = 207 minutes. 167 + their shortest | A1ft |
| (5) | |
| (10 marks) |
