Evaluate Division

Desicription

Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array.

Note:

The array size can be very large. Solution that uses too much extra space will not pass the judge.

Example:

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int[] nums = new int[] {1,2,3,3,3};
Solution solution = new Solution(nums);

// pick(3) should return either index 2, 3, or 4 randomly. Each index should have equal probability of returning.
solution.pick(3);

// pick(1) should return 0. Since in the array only nums[0] is equal to 1.
solution.pick(1);

Solution

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class Solution {
private:
std::unordered_map<std::string, std::string> father = std::unordered_map<std::string, std::string>{};
std::unordered_map<std::string, double> value = std::unordered_map<std::string, double>{};
std::unordered_map<std::string, std::set<std::pair<std::string, double>>> pairs{};

inline std::string find(const std::string& a) {
return father[a] == a ? a : father[a] = find(father[a]);
}
public:
std::vector<double> calcEquation(const std::vector<std::vector<std::string>>& equations, const std::vector<double>& values, const std::vector<std::vector<std::string>>& queries) {
for(unsigned long long i = 0; i < equations.size(); i++) {
father[equations[i][0]] = equations[i][0];
father[equations[i][1]] = equations[i][1];
pairs[equations[i][0]].insert({equations[i][1], values[i]});
pairs[equations[i][1]].insert({equations[i][0], 1.0f / values[i]});
}

for(unsigned long long i = 0; i < equations.size(); i++) {
auto a = find(equations[i][0]);
auto b = find(equations[i][1]);
if(a != b) {
father[a] = b;
}
}

std::queue<std::string> queue = std::queue<std::string>{};
for(const auto& pairIt : pairs) {
if(value.find(pairIt.first) != value.end()) {
continue;
}
value[pairIt.first] = 1.0f;
queue.push(value.begin()->first);
while(!queue.empty()) {
std::string current = queue.front();
queue.pop();
for(const auto& it : pairs[current]) {
if(value.find(it.first) != value.end()) {
continue;
} else {
value[it.first] = value[current] / it.second;
queue.push(it.first);
}
}
}
}

std::vector<double> res = std::vector<double>{};
for(const auto& it : queries) {
auto itA = value.find(it[0]);
auto itB = value.find(it[1]);
if(itA != value.end() && itB != value.end() && find(itA->first) == find(itB->first)) {
res.push_back(itA->second / itB -> second);
} else {
res.push_back(-1.0f);
}
}

return res;
}
};