lecture 12 - Amrita

# lecture 12 - Amrita - BACKTRACKING & BRANCH-BOUND Back...

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BACKTRACKING & BRANCH-BOUND

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Back Tracking If a criterion gets satisfied, when a particular sequence of elements is being considered, then one could go up to the maximum depth possible. If at some point down the line, criterion is not satisfied then we backtrack to previous stage, and make a different sequence of remaining elements and try further. Let the sequence be a 1 , a 2 , a 3 , a 4 , a 5 a 1 a 2 a 3 a 4 a 3 a 5
Back Tracking If a criterion gets satisfied, when a particular sequence of elements is being considered, then one could go up to the maximum depth possible. If at some point down the line, criterion is not satisfied then we backtrack to previous stage, and make a different sequence of remaining elements and try further. Let the sequence be a 1 , a 2 , a 3 , a 4 , a 5 a 1 a 2 a 3 a 4 a 3 a 5 (Say) Not possible Solution sequence

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All possible states are tried right from the beginning, and the sequence which does not satisfy gets bound a 1 a 2 a 3 a 4 a 5 a 2 a 3 a 4 a 5 a 3 a 4 a 5 a 3 a 5 a 5 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Back Tracking – Depth First – Breadth Later Effectively reduces average search time. Prevents the search from getting into exhaustive mode, because non- satisfaction of criterion if detected at an earlier stage results in immediate backtracking or getting bound from further growth. These strategies are generally useful for solving exhaustive search problems

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Illustration: Shortest distance Find the minimum distance path from S to T S A B C D T 4 5 2.5 1 5 2 1 1.2 3 2.8 Let us consider depth first search (Back Tracking)
Illustration: Shortest distance Find the minimum distance path from S to T S A B C D T 4 5 2.5 1 5 2 1 1.2 3 2.8 Let us start from S S

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lecture 12 - Amrita - BACKTRACKING & BRANCH-BOUND Back...

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