Create 1203.Sort-Items-by-Groups-Respecting-Dependencies.cpp

Author: wisdompeak

BFS/1203.Sort-Items-by-Groups-Respecting-Dependencies/1203.Sort-Items-by-Groups-Respecting-Dependencies.cpp

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+class Solution {
+public:
+ vector<int> sortItems(int n, int m, vector<int>& group, vector<vector<int>>& beforeItems) 
+ {
+ unordered_map<int, unordered_set<int>>groupItems;
+ int nextGroupId = m;
+
+ for (int i=0; i<n; i++)
+ {
+ if (group[i]==-1)
+ {
+ group[i] = nextGroupId;
+ nextGroupId += 1;
+ }
+ groupItems[group[i]].insert(i);
+ }
+
+ // build graph inside each group
+ unordered_map<int, unordered_set<int>>next;
+ unordered_map<int, int>inDegree;
+ for (int i=0; i<n; i++) 
+ for (int j: beforeItems[i])
+ {
+ if (group[i]!=group[j]) continue;
+ if (next[j].find(i)==next[j].end()) 
+ {
+ next[j].insert(i);
+ inDegree[i] += 1;
+ }
+ }
+ // sort nodes inside each group
+ unordered_map<int, vector<int>>groupItemsOrdered;
+ for (auto x: groupItems)
+ {
+ int groupId = x.first;
+ groupItemsOrdered[groupId] = topologySort(groupItems[groupId], next, inDegree);
+ if (groupItemsOrdered[groupId].size() != groupItems[groupId].size())
+ return {};
+ }
+
+ // build graph among groups
+ next.clear();
+ inDegree.clear();
+ for (int i=0; i<n; i++) 
+ for (int j: beforeItems[i])
+ {
+ if (group[i]==group[j]) continue;
+ if (next[group[j]].find(group[i])==next[group[j]].end()) 
+ {
+ next[group[j]].insert(group[i]);
+ inDegree[group[i]] += 1;
+ }
+ }
+ // sort groups
+ unordered_set<int>groups;
+ for (int i=0; i<n; i++) groups.insert(group[i]);
+ vector<int>groupOrdered = topologySort(groups, next, inDegree);
+
+ vector<int>rets;
+ for (int groupId: groupOrdered)
+ {
+ for (auto node: groupItemsOrdered[groupId])
+ rets.push_back(node);
+ }
+ return rets;
+ }
+
+ vector<int> topologySort (unordered_set<int>&nodes, unordered_map<int, unordered_set<int>>&next, unordered_map<int, int>&inDegree)
+ {
+ queue<int>q;
+ vector<int>ret;
+ for (auto node: nodes)
+ {
+ if (inDegree[node]==0)
+ q.push(node);
+ }
+ while (!q.empty())
+ {
+ int cur = q.front();
+ q.pop();
+ ret.push_back(cur); 
+ for (auto next: next[cur] )
+ {
+ inDegree[next] -= 1;
+ if (inDegree[next] == 0)
+ q.push(next);
+ }
+ }
+ 
+ if (ret.size()==nodes.size())
+ return ret;
+ else
+ return {};
+ }
+};