399. 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"] ].

The input is always valid. You may assume that evaluating the queries will result in no division by zero and there is no contradiction.

class Solution {
public:
vector<double> calcEquation(vector<pair<string, string>> equations,
vector<double>& values, vector<pair<string, string>> query)
{
unordered_map<string,unordered_map<string, double>> m;
vector<double> res;
for (int i = 0; i < values.size(); ++i)
{
m[equations[i].first].insert(make_pair(equations[i].second,values[i]));
if(values[i]!=0)
4000

m[equations[i].second].insert(make_pair(equations[i].first,1/values[i]));
}

for (auto i : query)
{
unordered_set<string> s;
double tmp = check(i.first,i.second,m,s);
if(tmp) res.push_back(tmp);
else res.push_back(-1);
}
return res;
}

double check(string up, string down,
unordered_map<string,unordered_map<string, double>> &m,
unordered_set<string> &s)
{
if(m[up].find(down) != m[up].end()) return m[up][down];
for (auto i : m[up])
{
if(s.find(i.first) == s.end())
{
s.insert(i.first);
double tmp = check(i.first,down,m,s);
if(tmp) return i.second*tmp;
}
}
return 0;
}
};