LeetCode 444. Sequence Reconstruction Sequence不连续

序列重构挑战

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探讨如何从一组子序列中唯一地重建原始序列，通过实例解析验证序列重构的可行性，深入理解子序列概念及其在算法中的应用。

Check whether the original sequence org can be uniquely reconstructed from the sequences in seqs. The org sequence is a permutation of the integers from 1 to n, with 1 ≤ n ≤ 104. Reconstruction means building a shortest common supersequence of the sequences in seqs (i.e., a shortest sequence so that all sequences in seqs are subsequences of it). Determine whether there is only one sequence that can be reconstructed from seqs and it is the org sequence.

Example 1:

Input: org = [1,2,3], seqs = [[1,2],[1,3]]
Output: false
Explanation: [1,2,3] is not the only one sequence that can be reconstructed, because [1,3,2] is also a valid sequence that can be reconstructed.

Example 2:

Input: org = [1,2,3], seqs = [[1,2]]
Output: false
Explanation: The reconstructed sequence can only be [1,2].

Example 3:

Input: org = [1,2,3], seqs = [[1,2],[1,3],[2,3]]
Output: true
Explanation: The sequences [1,2], [1,3], and [2,3] can uniquely reconstruct the original sequence [1,2,3].

Example 4:

Input: org = [4,1,5,2,6,3], seqs = [[5,2,6,3],[4,1,5,2]]
Output: true

Constraints:

1 <= n <= 10^4
org is a permutation of {1,2,...,n}.
seqs[i][j] fits in a 32-bit signed integer.

UPDATE (2017/1/8):
The seqs parameter had been changed to a list of list of strings (instead of a 2d array of strings). Please reload the code definition to get the latest changes.

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这题难点是理解题目，注意subsequence可以不连续，但是题目给的例子都是连续的，这点搞得非常困惑。。。如果不连续那这题的意思就清楚多了。。。

class Solution:
    def sequenceReconstruction(self, org, seqs):
        index = {num: i for i, num in enumerate([None] + org)}
        pairs = set(zip([None] + org, org))
        for seq in seqs:
            for a, b in zip([None] + seq, seq):
                if index[a] >= index.get(b, 0):
                    return False
                pairs.discard((a, b))
        return not pairs