alien_dictionary.cpp

published c++ code fails for this test case: ["zy","zx"]

cpp/neetcode_150/12_advanced_graphs/alien_dictionary.cpp

@@ -9,76 +9,88 @@
  Space: O(n)
 */
 
-class Solution {
-public:
- string alienOrder(vector<string>& words) {
- unordered_map<char, unordered_set<char>> graph;
+// create graph or adjacency list
+ unordered_map<char, unordered_set<char>> graph; // set to avoid duplicacy
  unordered_map<char, int> indegree;
-
- // initialize, find all unique letters
- for (int i = 0; i < words.size(); i++) {
- for (int j = 0; j < words[i].size(); j++) {
- char c = words[i][j];
+
+ for(auto word: words){
+ for(auto c : word){
  indegree[c] = 0;
  }
  }
-
- // build graph, record indegree, find all edges
- for (int i = 0; i < words.size() - 1; i++) {
- string word1 = words[i];
- string word2 = words[i + 1];
+
+ for(int i=0; i<words.size()-1; i++){
 
- // find first mismatch & insert into hash maps
- int length = min(word1.size(), word2.size());
- for (int j = 0; j < length; j++) {
- if (word1[j] != word2[j]) {
- unordered_set<char> s = graph[word1[j]];
- if (s.find(word2[j]) == s.end()) {
- graph[word1[j]].insert(word2[j]);
- indegree[word2[j]]++;
+ bool flag = false;
+ string s1 = words[i];
+ string s2 = words[i+1];
+
+ int len = min(s1.length(), s2.length());
+
+ for(int j=0; j<len; j++){
+
+ char ch1 = s1[j];
+ char ch2 = s2[j];
+
+ // if the char do not match
+ if(ch1 != ch2){
+
+ unordered_set<char> set;
+ if(graph.find(ch1) != graph.end()){
+
+ set = graph[ch1];
+
+ if(set.find(ch2) == set.end()){
+ set.insert(ch2);
+ graph[ch1] = set;
+ indegree[ch2]++;
+ }
+
+ }
+ else{
+ set.insert(ch2);
+ graph[ch1] = set;
+ indegree[ch2]++;
  }
+
+ flag = true;
  break;
  }
-
- if (j == length - 1 && word1.size() > word2.size()) {
- return "";
- }
  }
+ if(flag == false and (s1.length() > s2.length())) return "";
  }
-
- // bfs + topological sort
- string result = "";
- queue<char> q;
 
- for (auto it = indegree.begin(); it != indegree.end(); it++) {
- if (it->second == 0) {
-  q.push(it->first);
- }
+ queue<char> pq;
+
+ for(auto i : indegree){
+ if(i.second == 0) pq.push(i.first);
  }
 
- while (!q.empty()) {
- char c = q.front();
- q.pop();
- result += c;
+ string ans = "";
+ int count = 0;
+ while(pq.size()>0){
 
- if (graph[c].empty()) {
- continue;
- }
-
- unordered_set<char> edges = graph[c];
- for (auto it = edges.begin(); it != edges.end(); it++) {
- char edge = *it;
- indegree[edge]--;
- if (indegree[edge] == 0) {
- q.push(edge);
+ auto rem = pq.front();
+ pq.pop();
+
+ ans += rem;
+ count++;
+
+ if(graph[rem].empty()) continue;
+
+ if(graph.find(rem) != graph.end()){
+ unordered_set<char> nbrs = graph[rem];
+
+ for(char nbr : nbrs){
+ indegree[nbr]--;
+ if(indegree[nbr] == 0){
+ pq.push(nbr);
+ }
  }
  }
  }
-
- // check if it's cyclic
- if (result.size() < indegree.size()) {
- return "";
+
+ if(count == indegree.size()){
+ return ans;
  }
- return result;
- }
-};
+ return "";