leetcode 399. Evaluate Division 等式求解+典型的DFS深度优先遍历
2017-12-06 21:26
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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.
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.
题意很简单,就是做一个除法的计算,就是一个DFS深度优先遍历的实现
这道题的要点是可以使用后继结点来保存树结构,使用父亲节点也可以,别的都没有难点了
注意这里的set是为了防止陷入死循环
代码如下:
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.
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.
题意很简单,就是做一个除法的计算,就是一个DFS深度优先遍历的实现
这道题的要点是可以使用后继结点来保存树结构,使用父亲节点也可以,别的都没有难点了
注意这里的set是为了防止陷入死循环
代码如下:
#include <iostream> #include <vector> #include <map> #include <unordered_map> #include <set> #include <unordered_set> #include <queue> #include <stack> #include <string> #include <climits> #include <algorithm> #include <sstream> #include <functional> #include <bitset> #include <numeric> #include <cmath> #include <regex> using namespace std; class Solution { public: map<string, map<string, double>> m; vector<double> calcEquation(vector<pair<string, string>> equations, vector<double>& values, vector<pair<string, string>> query) { 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) m[equations[i].second].insert(make_pair(equations[i].first, 1 / values[i])); } for (auto i : query) { set<string> s; double tmp = check(i.first, i.second, s); res.push_back(tmp); } return res; } double check(string up, string down, set<string> &s) { if (m[up].find(down) != m[up].end()) return m[up][down]; else { for (auto i : m[up]) { if (s.find(i.first) == s.end()) { s.insert(i.first); double tmp = check(i.first, down, s); if (tmp != -1) return i.second*tmp; } } return -1; } } };
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