cgddrd · November 19, 2015 12:57 · Mar 24, 2013
diff --git a/StochasticUniversalSampling.java b/StochasticUniversalSampling.java
@@ -0,0 +1,42 @@
+public class StochasticUniversalSampling {
+
+    /**
+     *
+     * @param population - set of individuals' segments. Segment is equal to individual's fitness.
+     * @param n - number of individuals to choose from population.
+     * @return set of indexes, pointing to the chosen individuals in the population set
+     */
+    public int[] execute(double[] population, int n) {
+        // Calculate total fitness of population
+        double f = 0.0;
+        for (double segment : population) {
+            f += segment;
+        }
+        // Calculate distance between the pointers
+        double p = f / n;
+        // Pick random number between 0 and p
+        double start = Math.random() * p;
+        // Pick n individuals
+        int[] individuals = new int[n];
+        int index = 0;
+        double sum = population[index];
+        for (int i = 0; i < n; i++) {
+            // Determine pointer to a segment in the population
+            double pointer = start + i * p;
+            // Find segment, which corresponds to the pointer
+            if (sum >= pointer) {
+                individuals[i] = index;
+            } else {
+                for (++index; index < population.length; index++) {
+                    sum += population[index];
+                    if (sum >= pointer) {
+                        individuals[i] = index;
+                        break;
+                    }
+                }
+            }
+        }
+        // Return the set of indexes, pointing to the chosen individuals
+        return individuals;
+    }
+}