[剑指 Offer II 114. 外星文字典](拓扑排序)

Posted 2022-06-02 Harris-H

剑指 Offer II 114. 外星文字典(拓扑排序)

先按照相邻单词比较建图。

然后跑拓扑排序。

class Solution 
public:
    unordered_map<char, vector<char>> edges;
    unordered_map<char, int> indegrees;
    bool valid = true;

    string alienOrder(vector<string>& words) 
        int length = words.size();
        for (auto word : words) 
            int wordLength = word.size();
            for (int j = 0; j < wordLength; j++) 
                char c = word[j];
                if (!edges.count(c)) 
                    edges[c] = vector<char>();
                
            
        
        for (int i = 1; i < length && valid; i++) 
            addEdge(words[i - 1], words[i]);
        
        if (!valid) 
            return "";
        
        queue<char> qu;
        for (auto [u, _] : edges) 
            if (!indegrees.count(u)) 
                qu.emplace(u);
            
        
        string order;
        while (!qu.empty()) 
            char u = qu.front();
            qu.pop();
            order.push_back(u);
            for (char v : edges[u]) 
                indegrees[v]--;
                if (indegrees[v] == 0) 
                    qu.emplace(v);
                
            
        
        return order.size() == edges.size() ? order : "";
    

    void addEdge(string before, string after) 
        int length1 = before.size(), length2 = after.size();
        int length = min(length1, length2);
        int index = 0;
        while (index < length) 
            char c1 = before[index], c2 = after[index];
            if (c1 != c2) 
                edges[c1].emplace_back(c2);
                indegrees[c2] += 1;
                break;
            
            index++;
        
        if (index == length && length1 > length2) 
            valid = false;
        
    
;