{ "data": { "question": { "questionId": "3112", "questionFrontendId": "2867", "boundTopicId": null, "title": "Count Valid Paths in a Tree", "titleSlug": "count-valid-paths-in-a-tree", "content": "

There is an undirected tree with n nodes labeled from 1 to n. You are given the integer n and a 2D integer array edges of length n - 1, where edges[i] = [ui, vi] indicates that there is an edge between nodes ui and vi in the tree.

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Return the number of valid paths in the tree.

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A path (a, b) is valid if there exists exactly one prime number among the node labels in the path from a to b.

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Note that:

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Example 1:

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\nInput: n = 5, edges = [[1,2],[1,3],[2,4],[2,5]]\nOutput: 4\nExplanation: The pairs with exactly one prime number on the path between them are: \n- (1, 2) since the path from 1 to 2 contains prime number 2. \n- (1, 3) since the path from 1 to 3 contains prime number 3.\n- (1, 4) since the path from 1 to 4 contains prime number 2.\n- (2, 4) since the path from 2 to 4 contains prime number 2.\nIt can be shown that there are only 4 valid paths.\n
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Example 2:

\n\"\"\n
\nInput: n = 6, edges = [[1,2],[1,3],[2,4],[3,5],[3,6]]\nOutput: 6\nExplanation: The pairs with exactly one prime number on the path between them are: \n- (1, 2) since the path from 1 to 2 contains prime number 2.\n- (1, 3) since the path from 1 to 3 contains prime number 3.\n- (1, 4) since the path from 1 to 4 contains prime number 2.\n- (1, 6) since the path from 1 to 6 contains prime number 3.\n- (2, 4) since the path from 2 to 4 contains prime number 2.\n- (3, 6) since the path from 3 to 6 contains prime number 3.\nIt can be shown that there are only 6 valid paths.\n
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Constraints:

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Python 3.10.

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