README.md

剑指 Offer II 115. 重建序列

题目描述

请判断原始的序列 org 是否可以从序列集 seqs 中唯一地 重建 。

序列 org 是 1 到 n 整数的排列，其中 1 ≤ n ≤ 10⁴。重建 是指在序列集 seqs 中构建最短的公共超序列，即  seqs 中的任意序列都是该最短序列的子序列。

 

示例 1：

输入: org = [1,2,3], seqs = [[1,2],[1,3]]
输出: false
解释：[1,2,3] 不是可以被重建的唯一的序列，因为 [1,3,2] 也是一个合法的序列。

示例 2：

输入: org = [1,2,3], seqs = [[1,2]]
输出: false
解释：可以重建的序列只有 [1,2]。

示例 3：

输入: org = [1,2,3], seqs = [[1,2],[1,3],[2,3]]
输出: true
解释：序列 [1,2], [1,3] 和 [2,3] 可以被唯一地重建为原始的序列 [1,2,3]。

示例 4：

输入: org = [4,1,5,2,6,3], seqs = [[5,2,6,3],[4,1,5,2]]
输出: true

 

提示：

• 1 <= n <= 104
• org 是数字 1 到 n 的一个排列
• 1 <= segs[i].length <= 105
• seqs[i][j] 是 32 位有符号整数

 

注意：本题与主站 444 题相同：https://leetcode-cn.com/problems/sequence-reconstruction/

解法

拓扑排序，BFS 实现。

Python3

class Solution:
    def sequenceReconstruction(self, org: List[int], seqs: List[List[int]]) -> bool:
        n = len(org)
        nums = set()
        for seq in seqs:
            for num in seq:
                if num < 1 or num > n:
                    return False
                nums.add(num)
        if len(nums) < n:
            return False

        edges = collections.defaultdict(list)
        indegree = [0] * (n + 1)
        for seq in seqs:
            i = seq[0]
            for j in seq[1:]:
                edges[i].append(j)
                indegree[j] += 1
                i = j
        q = collections.deque()
        for i in range(1, n + 1):
            if indegree[i] == 0:
                q.append(i)
        cnt = 0
        while q:
            if len(q) > 1 or org[cnt] != q[0]:
                return False
            i = q.popleft()
            cnt += 1
            for j in edges[i]:
                indegree[j] -= 1
                if indegree[j] == 0:
                    q.append(j)
        return cnt == n

Java

class Solution {
    public boolean sequenceReconstruction(int[] org, List<List<Integer>> seqs) {
        int n = org.length;
        Set<Integer> nums = new HashSet<>();
        for (List<Integer> seq : seqs) {
            for (int num : seq) {
                if (num < 1 || num > n) {
                    return false;
                }
                nums.add(num);
            }
        }
        if (nums.size() < n) {
            return false;
        }
        List<Integer>[] edges = new List[n + 1];
        for (int i = 0; i < edges.length; ++i) {
            edges[i] = new ArrayList<>();
        }
        int[] indegree = new int[n + 1];
        for (List<Integer> seq : seqs) {
            int i = seq.get(0);
            for (int j = 1; j < seq.size(); ++j) {
                edges[i].add(seq.get(j));
                ++indegree[seq.get(j)];
                i = seq.get(j);
            }
        }
        Queue<Integer> q = new LinkedList<>();
        for (int i = 1; i <= n; ++i) {
            if (indegree[i] == 0) {
                q.offer(i);
            }
        }
        int cnt = 0;
        while (!q.isEmpty()) {
            if (q.size() > 1 || q.peek() != org[cnt]) {
                return false;
            }
            ++cnt;
            int i = q.poll();
            for (int j : edges[i]) {
                --indegree[j];
                if (indegree[j] == 0) {
                    q.offer(j);
                }
            }
        }
        return cnt == n;
    }
}

C++

class Solution {
public:
    bool sequenceReconstruction(vector<int>& org, vector<vector<int>>& seqs) {
        int n = org.size();
        unordered_set<int> nums;
        for (auto& seq : seqs)
        {
            for (int num : seq)
            {
                if (num < 1 || num > n) return false;
                nums.insert(num);
            }
        }
        if (nums.size() < n) return false;
        vector<vector<int>> edges(n + 1);
        vector<int> indegree(n + 1);
        for (auto& seq : seqs)
        {
            int i = seq[0];
            for (int j = 1; j < seq.size(); ++j)
            {
                edges[i].push_back(seq[j]);
                ++indegree[seq[j]];
                i = seq[j];
            }
        }
        queue<int> q;
        for (int i = 1; i <= n; ++i)
        {
            if (indegree[i] == 0) q.push(i);
        }
        int cnt = 0;
        while (!q.empty())
        {
            if (q.size() > 1 || q.front() != org[cnt]) return false;
            ++cnt;
            int i = q.front();
            q.pop();
            for (int j : edges[i])
            {
                --indegree[j];
                if (indegree[j] == 0) q.push(j);
            }
        }
        return cnt == n;
    }
};

Go

func sequenceReconstruction(org []int, seqs [][]int) bool {
	n := len(org)
	nums := make(map[int]bool)
	for _, seq := range seqs {
		for _, num := range seq {
			if num < 1 || num > n {
				return false
			}
			nums[num] = true
		}
	}
	if len(nums) < n {
		return false
	}
	edges := make([][]int, n+1)
	indegree := make([]int, n+1)
	for _, seq := range seqs {
		i := seq[0]
		for _, j := range seq[1:] {
			edges[i] = append(edges[i], j)
			indegree[j]++
			i = j
		}
	}
	var q []int
	for i := 1; i <= n; i++ {
		if indegree[i] == 0 {
			q = append(q, i)
		}
	}
	cnt := 0
	for len(q) > 0 {
		if len(q) > 1 || org[cnt] != q[0] {
			return false
		}
		i := q[0]
		q = q[1:]
		cnt++
		for _, j := range edges[i] {
			indegree[j]--
			if indegree[j] == 0 {
				q = append(q, j)
			}
		}
	}
	return cnt == n
}

...