[LeetCode]444. Sequence Reconstruction

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

思路：

遍历seqs中的每一个seq。每一个seq中，后一个元素是前一个元素的successor。建立一个unordered_map， 记录每一个元素的successor。建立一个unordered_mao indegree， 记录每个点的入度。org里第一个元素的入度应该为零！利用拓扑排序（Topological Sort）,每次找出入度为零的元素， 然后所有次元素的后继元素的入度减一，找到新的入度为零的元素。拓扑排序生成的数组顺序应该与org 相同。

转载于:https://www.cnblogs.com/superd/p/6120508.html