moved Kosaraju for SCC computation to "graph"

Author: yanntm

fr.lip6.move.gal.structural/src/fr/lip6/move/gal/graph/Kosaraju.java

@@ -0,0 +1,69 @@
+package fr.lip6.move.gal.graph;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.Stack;
+
+import android.util.SparseIntArray;
+import fr.lip6.move.gal.util.IntMatrixCol;
+
+public class Kosaraju {
+
+public static List<List<Integer>> searchForSCC(IntMatrixCol graph) {
+// This part implements Kosaraju to find SCC
+// not the best time complexity algo for that, but enough for us.
+Stack<Integer> stack = new Stack<>();
+Set<Integer> visited = new HashSet<>();
+
+// derecursed version uses a todo stack
+Stack<Integer> todo = new Stack<>();
+for (int p = 0; p < graph.getColumnCount(); p++) {
+todo.add(p);
+}
+while (!todo.isEmpty()) {
+int p = todo.pop();
+if (p == -1) {
+stack.push(todo.pop());
+continue;
+}
+SparseIntArray col = graph.getColumn(p);
+if (col.size() > 0) {
+if (!visited.add(p)) {
+continue;
+}
+todo.push(p);
+todo.push(-1);
+for (int i = 0; i < col.size(); i++) {
+todo.push(col.keyAt(i));
+}
+}
+}
+
+List<List<Integer>> sccs = new ArrayList<>();
+List<Integer> curScc = new ArrayList<>();
+visited.clear();
+graph = graph.transpose();
+while (!stack.isEmpty()) {
+int cur = stack.pop();
+visitNode(graph, curScc, cur, visited);
+if (!curScc.isEmpty()) {
+sccs.add(curScc);
+curScc = new ArrayList<>();
+}
+}
+return sccs;
+}
+
+private static void visitNode(IntMatrixCol graph, List<Integer> curScc, int cur, Set<Integer> visited) {
+if (visited.add(cur)) {
+curScc.add(cur);
+SparseIntArray col = graph.getColumn(cur);
+for (int i = 0; i < col.size(); i++) {
+visitNode(graph, curScc, col.keyAt(i), visited);
+}
+}
+}
+
+}