这道题我感觉是LintCode里面Topological Sorting里最难Pass的,虽然思路不难,但是很多测试用例过不了。
思路:基于topological sorting。每次都要确定queue.size()是1, 并且还要判断是不是跟给出的org数组一样。否则返回false。
代码如下:
class Solution {
public:
/** * @param org: a permutation of the integers from 1 to n * @param seqs: a list of sequences * @return: true if it can be reconstructed only one or false */
bool sequenceReconstruction(vector<int> &org, vector<vector<int>> &seqs) {
map<int, set<int>> neighborMap;
map<int, int> indegreeMap;
queue<int> q;
if (org.empty()) {
if (seqs.empty()) return true;
if ((seqs.size()==1) && (seqs[0].empty())) return true;
}
if (org.empty() || seqs.empty() || seqs[0].empty())
return false;
for (auto v : seqs) {
for (int i=0; i<v.size()-1; ++i) {
//only when we find a new neighbor pair, add to the neighborMap and indegreeMap
if (neighborMap[v[i]].find(v[i+1])==neighborMap[v[i]].end()){
neighborMap[v[i]].insert(v[i+1]);
if (indegreeMap.find(v[i+1])!=indegreeMap.end()) {
indegreeMap[v[i+1]]++;
} else {
indegreeMap[v[i+1]]=1;
}
}
}
}
int totalNum=0;
for (int i=1; i<=org.size(); ++i) {
if (indegreeMap[i]==0) {
q.push(i);
}
}
int index=0;
while(q.size()==1) {
// for (int i=0; i<q.size(); ++i) { //size should be 1, so we don't need the for loop
int n=q.front();
q.pop();
if (n!=org[index++])
return false;
for (auto i : neighborMap[n]) {
indegreeMap[i]--;
if (indegreeMap[i]==0) {
q.push(i);
}
}
}
return index==org.size();
}
};
注意输入测试例子:
1. []
[[]]
2. [5,3,2,4,1]
[[5,3,2,4],[4,1],[1],[3],[2,4],[1,1000000000]]
3. [4,1,5,2,6,3]
[[5,2,6,3],[4,1,5,2]]
4. [1,2,3]
[[1,2],[1,3],[2,3]]