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POWhy is my Depth First Search Implementation Broken
 

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  1. POWhy is my Depth First Search Implementation Broken
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    <p>I've been experimenting with different ways of implementing depth first search. I've found a few working ways, but they involved some rather tedious dictionary work. I've developed a new idea using lists, but the actions this implementation returns don't match the desired result. I'll try to comment the code as clearly as I can: </p> <pre><code>start = problem.getStartState() ## returns an (x, y) tuple children = problem.getSuccessors(start) ##returns the children of a parent node in ((start state), action, cost) format. stack = Stack() ##creates a Stack (LIFO) data structure visited = [] ##list of visited nodes visited.append(start) for child in children: stack.push((child, [], [], 0)) ##push children to fringe in the format of (child, while stack: ##path taken, actions taken, cost) parent = stack.pop() node = parent[0] if parent[0] in visited: continue visited.append(parent[0]) path = parent[1] + [node[0]] ##assigns previous path/actions/cost to new actions = parent[2] + [node[1]] ##node, creating a cumulative, ordered list of print actions ##the path/actions and a cumulative cost cost = parent[3] + node[2] if problem.isGoalState(node[0]): print parent[2] return parent[2] ## returns list of actions children = problem.getSuccessors(node[0]) if children != []: for child in children: stack.push((child, path, actions, cost)) ##assigns cumulative lists to child </code></pre> <p>Anyone see where my problems might lie in this implementation? BTW, I know DFS is an inefficient algorithm for most cases. But once I get this implementation right, it should be able to cross over to other search algorithms by simply changing the data structure that stores the children of the parent node. </p>
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    1. COCan you give an example of expected output vs your output?
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    2. COYou have a code smell where you treat the "start" node differently then the other nodes when iterating its children. I'm betting the bug is connected to this.
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      1. USamit
    3. COWell, it's very problem specific and probably wouldn't make too much sense without a ton of specifications. Basically, I am expecting a list of actions that will lead me on the correct path to the goal destination. The problem reaches the goal destination (otherwise it would return nothing), but the list of actions somehow has me backtracking over already covered ground (despite my visited list) and stopping at a dead end.
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