Add a solution to Evaluate Division

Graph/EvaluateDivision.swift

@@ -0,0 +1,62 @@
+/**
+ * Question Link: https://leetcode.com/problems/evaluate-division/
+ * Primary idea: Classic Union Find. Update roots and values while building the graph.
+ * 
+ * Time Complexity: O((M + N) * logN), Space Complexity: O(N)
+ *
+ */
+
+class EvaluateDivision {
+    func calcEquation(_ equations: [[String]], _ values: [Double], _ queries: [[String]]) -> [Double] {
+        var res = [Double]()
+        var graph = union(equations, values)
+
+        for query in queries {
+            if graph[query[0]] == nil || graph[query[1]] == nil {
+                res.append(-1.0)
+                continue
+            }
+
+            let left = find(&graph, query[0])
+            let right = find(&graph, query[1])
+
+            if left.0 != right.0 {
+                res.append(-1.0)
+            } else {
+                res.append(left.1 / right.1)
+            }
+        }
+
+        return res
+    }
+
+    private func find(_ roots: inout [String: (String, Double)], _ node: String) -> (String, Double) {
+        if roots[node] == nil {
+            roots[node] = (node, 1)
+        }
+
+        var n = roots[node]!.0
+
+        while n != roots[n]!.0 {
+            roots[node] = (roots[n]!.0, roots[n]!.1 * roots[node]!.1)
+            n = roots[n]!.0
+        }
+
+        return roots[node]!
+    }
+
+    private func union(_ equations: [[String]], _ values: [Double]) -> [String: (String, Double)] {
+        var res = [String: (String, Double)]()
+
+        for i in 0..<equations.count {
+            let left = find(&res, equations[i][0])
+            let right = find(&res, equations[i][1])
+
+            if left.0 != right.0 {
+                res[left.0] = (right.0, values[i] * right.1 / left.1)
+            }
+        }
+
+        return res
+    }
+}