Evaluate Division

Equations are given in the format A / B = k, where A and B are variables represented as strings, and k is a real number (floating point number). Given some queries, return the answers. If the answer does not exist, return -1.0.Example:Given a / b = 2.0, b / c = 3.0. queries are: a / c = ?, b / a = ?, a / e = ?, a / a = ?, x / x = ? . return [6.0, 0.5, -1.0, 1.0, -1.0 ].The input is: vector<pair<string, string>> equations, vector<double>& values, vector<pair<string, string>> queries , where equations.size() == values.size(), and the values are positive. This represents the equations. Return vector<double>.

According to the example above:

equations = [ ["a", "b"], ["b", "c"] ],values = [2.0, 3.0],queries = [ ["a", "c"], ["b", "a"], ["a", "e"], ["a", "a"], ["x", "x"] ]. 

解答

class Solution {public:    vector<double> calcEquation(vector<pair<string, string>> equations, vector<double>& values, vector<pair<string, string>> queries) {        unordered_map<string, Node*> map;        vector<double> res;        for (int i = 0; i < equations.size(); i ++) {            string s1 = equations[i].first, s2 = equations[i].second;            if (map.count(s1) == 0 && map.count(s2) == 0) {                map[s1] = new Node();                map[s2] = new Node();                map[s1] -> value = values[i];                map[s2] -> value = 1;                map[s1] -> parent = map[s2];            } else if (map.count(s1) == 0) {                map[s1] = new Node();                map[s1] -> value = map[s2] -> value * values[i];                map[s1] -> parent = map[s2];            } else if (map.count(s2) == 0) {                map[s2] = new Node();                map[s2] -> value = map[s1] -> value / values[i];                map[s2] -> parent = map[s1];            } else {                unionNodes(map[s1], map[s2], values[i], map);            }        }        for (auto query : queries) {            if (map.count(query.first) == 0 || map.count(query.second) == 0 || findParent(map[query.first]) != findParent(map[query.second]))                res.push_back(-1);            else                res.push_back(map[query.first] -> value / map[query.second] -> value);        }        return res;    }private:    struct Node {        Node* parent;        double value = 0.0;        Node()  {parent = this;}    };    void unionNodes(Node* node1, Node* node2, double num, unordered_map<string, Node*>& map) {        Node* parent1 = findParent(node1), *parent2 = findParent(node2);        double ratio = node2 -> value * num / node1 -> value;        for (auto it = map.begin(); it != map.end(); it ++)            if (findParent(it -> second) == parent1)                it -> second -> value *= ratio;        parent1 -> parent = parent2;    }    Node* findParent(Node* node) {        if (node -> parent == node)            return node;        node -> parent = findParent(node -> parent);        return node -> parent;    }};