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Answers for “在动态规划中,重叠子问题是什么?”

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Overlapping subproblems occur when the same smaller problem is solved multiple times during a recursive process. The Fibonacci tree makes this concrete by showing repeated calls such as fib(2) and fib(3), which cause redundant computation.

Conditions: The problem can be solved recursively.; The same subproblems appear multiple times in the recursion tree.

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The Fibonacci recursion tree demonstrates repeated computation by showing that the same subproblems are solved multiple times. For example, when computing the fifth Fibonacci number, the tree contains duplicated subcalls such as fib(2) and fib(3).

Conditions: The problem is being solved recursively.; The recursive decomposition revisits the same subproblem multiple times.

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The San Francisco to San Diego route can be split at Los Angeles because the problem exhibits optimal substructure. Once the shortest SF→LA and LA→SD segments are known, they combine to give the shortest SF→SD route.

Conditions: The example assumes the overall route passes through Los Angeles.; The narrator states that finding the shortest subroutes guarantees the overall shortest route in this example.

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Optimal substructure means that the optimal solution to the overall problem can be constructed by efficiently combining the optimal solutions of its subproblems. In the route example, once the shortest SF→LA and LA→SD segments are known, they combine to give the shortest SF→SD route.

Conditions: The problem can be divided into subproblems.; The optimal solution of the main problem depends on the optimal solutions of its subproblems.

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A problem is a dynamic programming problem if it satisfies two conditions: optimal substructure and overlapping subproblems. Optimal substructure means the optimal solution to the overall problem can be constructed from the optimal solutions of its subproblems.

Conditions: The problem can be solved using an algorithmic approach.; The problem can be divided into subproblems.