Let's walk through an example of the A* algorithm to find the shortest path between two points in a graph.
Suppose we have a map with the following nodes and connections:
A --5--> B --4--> C
| ^ ^
2 3 6
v | |
D ----- E --2-- F
We want to find the shortest path from node A to node F using the A* algorithm. We will assume that the cost of moving from one node to an adjacent node is equal to the distance between them.
- Initialize the open list with the start node A and the closed list as empty.
Open: A Closed:
- Select the node with the lowest f-score (estimated total cost) from the open list, which is A in this case. Add A to the closed list.
Open: Closed: A
- Expand the neighbors of A and calculate their f-scores. Add them to the open list if they are not already in the closed list. Assign A as their parent.
Open: B (f=7) Closed: A
- Select the node with the lowest f-score from the open list, which is B in this case. Add B to the closed list.
Open: Closed: A, B
- Expand the neighbors of B and calculate their f-scores. Add them to the open list if they are not already in the closed list. Assign B as their parent.
Open: D (f=8), C (f=11), E (f=10) Closed: A, B
- Select the node with the lowest f-score from the open list, which is D in this case. Add D to the closed list.
Open: C (f=11), E (f=10) Closed: A, B, D
- Expand the neighbors of D and calculate their f-scores. Add them to the open list if they are not already in the closed list. Assign D as their parent.
Open: E (f=10), B (f=11), C (f=11) Closed: A, B, D
- Select the node with the lowest f-score from the open list, which is E in this case. Add E to the closed list.
Open: B (f=11), C (f=11), F (f=12) Closed: A, B, D, E
- Expand the neighbors of E and calculate their f-scores. Add them to the open list if they are not already in the closed list. Assign E as their parent.
Open: F (f=12), B (f=11), C (f=11) Closed: A, B, D, E
- Select the node with the lowest f-score from the open list, which is B in this case. Add B to the closed list.
Open: C (f=11), F (f=12)
Closed: A, B, D, E, B
- Expand the neighbors of B and calculate their f-scores. Add them to the open list if they are not already in the closed list. Assign B as their parent.
Open: C (f=11), F (f=12)
Closed: A, B, D, E, B
- Select the node with the lowest f-score from the open list
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