A*-search Algorithm in Artificial Intelligence

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Questions and Answers

What data structure is used to store the list in Breadth First Search?

  • Heap
  • Stack
  • Linked List
  • Queue (correct)

Which search technique guarantees to find a solution and keeps every node in memory?

  • Breadth First Search (correct)
  • Uniform Cost Search
  • A* Search
  • Depth-First Search

What property must hold true for every node in Uniform Cost Search to find the cheapest solution?

  • $g(successor(n)) < g(n)$
  • $g(successor(n)) \geq g(n)$ (correct)
  • $g(successor(n)) > g(n)$
  • $g(successor(n)) = g(n)$

Which search algorithm ensures the shortest path to the goal in terms of cost?

<p>Uniform Cost Search (A)</p> Signup and view all the answers

Which search algorithm expands one of the nodes at the deepest level of the tree?

<p>Depth-First Search (B)</p> Signup and view all the answers

What is the evaluation function used in A* search algorithm?

<p>f(n) = h(n) + g(n) (C)</p> Signup and view all the answers

In A* search, what does the function g(n) represent?

<p>Cost of path from initial state to node n (A)</p> Signup and view all the answers

In which search technique are successors put at the end of a queue for expansion?

<p>Breadth First Search (D)</p> Signup and view all the answers

Which property of A* search ensures that it guarantees reaching the goal state?

<p>Completeness (C)</p> Signup and view all the answers

What is the worst-case time and space complexity of heuristic algorithms like A* search?

<p>Exponential (D)</p> Signup and view all the answers

Based on its properties, is A* search algorithm optimal?

<p>Yes, if the heuristic function is admissible (D)</p> Signup and view all the answers

Which memory-related issue arises when using A* search algorithm?

<p>Keeps all generated nodes in memory (B)</p> Signup and view all the answers

What data structure can be used to implement Depth-first search?

<p>Stack (D)</p> Signup and view all the answers

Which type of spaces does Depth-first search fail in?

<p>Infinite-depth spaces, spaces with loops (D)</p> Signup and view all the answers

What would improve search efficiency greatly according to the text?

<p>Ordering choices based on heuristics (C)</p> Signup and view all the answers

What does the heuristic function h(n) estimate in A* search?

<p>The cost of the path from the start state to node n (B)</p> Signup and view all the answers

How does A* search differ from Best First Search?

<p>A* search uses a heuristic to estimate the cost of the path, Best First Search doesn't (D)</p> Signup and view all the answers

What property makes Depth-first search incomplete and not optimal?

<p>May fail in infinite-depth spaces (B)</p> Signup and view all the answers

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Study Notes

Search Strategies

  • Informed search strategies use domain knowledge to order choices and explore the most promising paths first.
  • Best First Search:
    • Uses a heuristic function, h(n), to estimate the goodness of a node.
    • Estimates the cost of the path from the current state to a goal state.
    • Expands all nodes on a given level of the search tree before moving to the next level.
    • Implemented using a queue data structure.
    • Properties: takes space, optimal, and complete.
  • Uniform Cost Search:
    • Modifies Best First Search to find the shortest path to the goal in terms of cost.
    • Expands the least-cost unexpanded node.
    • Implemented using a priority queue ordered by path cost.
    • Properties: finds the cheapest solution, takes space, and has a cost that never decreases along the path.
  • Expands one of the nodes at the deepest level of the tree.
  • Implemented using a stack data structure.
  • Properties: incomplete, not optimal, fails in infinite depth spaces, and spaces with loops.

A* Search Algorithm

  • Considers both the estimated cost of getting from the current node to the goal node (h(n)) and the cost of getting from the initial node to the current node (g(n)).
  • Evaluation function: f(n) = h(n) + g(n).
  • Implemented by expanding the node with the lowest evaluation function.
  • Properties: complete, optimal, and optimally efficient for any given admissible heuristic function.
  • Takes memory and has exponential time and space complexity in the worst case.
  • The quality of the heuristic function affects the time and space complexity.

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