Evaluate division

Author: Tushar Roy

src/com/interview/graph/EvaluateDivison.java

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+package com.interview.graph;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Date 10/31/2016
+ * @author Tushar Roy
+ *
+ * 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.
+ *
+ * Solution
+ * Do Flyod warshall algorithm initialized as values between equations. Do Flyod Warshall to create
+ * all possible paths b/w two strings.
+ *
+ * Time complexity O(n * n * n) + O(m)
+ * where n is total number of strings in equations and m is total number of queries
+ *
+ * Reference
+ * https://leetcode.com/problems/evaluate-division/
+ */
+public class EvaluateDivison {
+    public double[] calcEquation(String[][] equations, double[] values, String[][] queries) {
+        if (equations.length == 0) {
+            return new double[0];
+        }
+        Map<String, Integer> index = new HashMap<>();
+        int count = 0;
+        for (int i = 0; i < equations.length; i++) {
+            String first = equations[i][0];
+            String second = equations[i][1];
+            if (!index.containsKey(first)) {
+                index.put(first, count++);
+            }
+            if (!index.containsKey(second)) {
+                index.put(second, count++);
+            }
+        }
+
+        double graph[][] = new double[count][count];
+        for (int i = 0; i < graph.length; i++) {
+            for (int j = 0; j < graph[i].length; j++) {
+                graph[i][j] = -1;
+            }
+        }
+
+        for (int i = 0; i < equations.length; i++) {
+            String first = equations[i][0];
+            String second = equations[i][1];
+            int i1 = index.get(first);
+            int i2 = index.get(second);
+            graph[i1][i1] = graph[i2][i2] = 1.0;
+            graph[i1][i2] = values[i];
+            graph[i2][i1] = 1/values[i];
+        }
+
+        for (int i = 0 ; i < graph.length; i++) {
+            for (int j = 0; j < graph.length; j++) {
+                if (graph[i][j] != -1) {
+                    continue;
+                }
+                for (int k = 0; k < graph.length; k++) {
+                    if (graph[i][k] == -1 || graph[k][j] == -1) {
+                        continue;
+                    }
+                    graph[i][j] = graph[i][k] * graph[k][j];
+                }
+            }
+        }
+
+        double[] result = new double[queries.length];
+        for (int i = 0; i < queries.length; i++) {
+            String first = queries[i][0];
+            String second = queries[i][1];
+            if (!index.containsKey(first) || !index.containsKey(second)) {
+                result[i] = -1;
+            } else {
+                int i1 = index.get(first);
+                int i2 = index.get(second);
+                result[i] = graph[i1][i2];
+            }
+        }
+
+        return result;
+    }
+}