399. Evaluate Division

Description

image-20210814211436494

image-20210814211447126

Solution

Record each equations’ string name and its corresponding index, used later.

Then do a floyd search to all strings, find their division.

Code

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class Solution {
public:
    vector<double> calcEquation(vector<vector<string>>& equations, vector<double>& values, vector<vector<string>>& queries) {
        vector<string> names;
        unordered_map<string, unordered_map<string, double>> Map;
        for(int i = 0; i < equations.size(); i++){
            if(Map.find(equations[i][0]) == Map.end()){
                Map[equations[i][0]][equations[i][0]] = 1.0;
                names.push_back(equations[i][0]);
            }
            if(Map.find(equations[i][1]) == Map.end()){
                Map[equations[i][1]][equations[i][1]] = 1.0;
                names.push_back(equations[i][1]);
            }
            Map[equations[i][0]][equations[i][1]] = values[i];
            Map[equations[i][1]][equations[i][0]] = 1.0/values[i];
        }
        
        for(int k = 0;k < Map.size();k++){
            for(int i = 0; i < Map.size();i++){
                for(int j = 0; j < Map.size(); j++){
                    if(i == j || i == k || j == k)
                        continue;
                    string a = names[i], b= names[j], c= names[k];
                    if(Map[a].find(c) != Map[a].end() && Map[b].find(c) != Map[b].end()){
                        Map[a][b] = Map[a][c] / Map[b][c];
                        Map[b][a] = Map[b][c] / Map[a][c];
                    }
                }
            }
        }
        vector<double> res;
        for(int i = 0; i < queries.size(); i++){
            string a = queries[i][0], b = queries[i][1];
            if(Map.find(a) == Map.end() || Map.find(b) == Map.end())
                res.push_back(-1);
            else if(Map[a].find(b) == Map[a].end())
                res.push_back(-1);
            else
                res.push_back(Map[a][b]);
        }
        return res;
    }
};