[BFS] Add a solution to Evaluate Division

Author: soapyigu

BFS/EvaluateDivision.swift

@@ -0,0 +1,75 @@
+/**
+ * Question Link: https://leetcode.com/problems/evaluate-division/
+ * Primary idea: Build dict to maintain divide result, and use BFS to get specific query value
+ * 
+ * Time Complexity: O(n^2), Space Complexity: O(n)
+ *
+ */
+
+class EvaluateDivision {
+    func calcEquation(_ equations: [[String]], _ values: [Double], _ queries: [[String]]) -> [Double] {
+        let dict = initDict(equations, values)
+        var rest = [Double]()
+        
+        for query in queries {
+            guard let _ = dict[query.first!], let _ = dict[query.last!] else {
+                rest.append(-1.0)
+                continue
+            }
+            
+            bfs(query, dict, &rest)
+        }
+        
+        return rest
+    }
+    
+    fileprivate func initDict(_ equations: [[String]], _ values: [Double]) -> [String: [(String, Double)]] {
+        var dict = [String: [(String, Double)]]()
+        
+        for (i, equation) in equations.enumerated() {
+            let dividend = equation.first!, divisor = equation.last!, divideRes = values[i]
+            
+            insert(dividend, divisor, divideRes, to: &dict)
+            insert(divisor, dividend, 1.0 / divideRes, to: &dict)
+        }
+        
+        return dict
+    }
+    
+    fileprivate func insert(_ dividend: String, _ divisor: String, _ divideRes: Double, to dict: inout [String: [(String, Double)]]) {
+        if dict[dividend] == nil {
+            dict[dividend] = [(divisor, divideRes)]
+        } else {
+            dict[dividend]!.append((divisor, divideRes))
+        }
+    }
+    
+    fileprivate func bfs(_ query: [String], _ dict: [String: [(String, Double)]], _ rest: inout [Double]) {
+        var visited = Set([query.first!])
+        var qStrs = [query.first!]
+        var qVals = [1.0]
+
+        while !qStrs.isEmpty {
+            let currentStr = qStrs.removeFirst()
+            let currentVal = qVals.removeFirst()
+
+            if currentStr == query.last! {
+                rest.append(currentVal)
+                return
+            }
+
+            for (str, val) in dict[currentStr]! {
+                guard !visited.contains(str) else {
+                    continue
+                }
+
+                visited.insert(str)
+                qStrs.append(str)
+                qVals.append(currentVal * val)
+            }
+
+
+            rest.append(-1.0)
+        }
+    }
+}

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 247 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
+[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 248 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
 
 
 ## Array
@@ -241,6 +241,7 @@
 ## Breadth-first search
 | Title | Solution | Difficulty | Time | Space |
 | ----- | -------- | ---------- | ---- | ----- |
+[Evaluate Division](https://leetcode.com/problems/evaluate-division/)| [Swift](./BFS/EvaluateDivision.swift)| Medium| O(n^2)| O(n)|
 [Shortest Distance from All Buildings](https://leetcode.com/problems/shortest-distance-from-all-buildings/)| [Swift](./BFS/ShortestDistanceAllBuildings.swift)| Hard| O((mn)^2)| O(mn)|
 
 ## Math