Add backtracking and stack related algorithms.

Author: rayworks

src/main/java/org/sean/backtracking/AllSubsets.java

@@ -0,0 +1,48 @@
+package org.sean.backtracking;
+
+/**
+ * Created by Sean on 6/4/17.
+ */
+public class AllSubsets extends BackTrack {
+
+    public static void main(String[] args) {
+        int[] a = new int[10];
+
+        AllSubsets as = new AllSubsets();
+        as.backTrack(a, 0, 3);
+    }
+
+    @Override
+    protected void unmakeMove(int[] solutionVec, int pos, int size) {
+
+    }
+
+    @Override
+    protected void makeMove(int[] solutionVec, int pos, int size) {
+
+    }
+
+    @Override
+    protected int constructCandidates(int[] solutionVec, int pos, int size, int[] outCandidates) {
+        outCandidates[0] = 1;
+        outCandidates[1] = 0;
+
+        return 2;
+    }
+
+    @Override
+    protected void processSolution(int[] solutionVec, int pos, int inputSize) {
+        System.out.print("{");
+        for (int i = 1; i <= pos; i++) {
+            if (solutionVec[i] == 1) {
+                System.out.print(String.format(" %d", i));
+            }
+        }
+        System.out.print(" }\n");
+    }
+
+    @Override
+    protected boolean isASolution(int[] solutionVec, int pos, int inputSize) {
+        return pos == inputSize;
+    }
+}

src/main/java/org/sean/backtracking/BackTrack.java

@@ -0,0 +1,43 @@
+package org.sean.backtracking;
+
+/**
+ * Created by Sean on 6/4/17.
+ */
+public abstract class BackTrack {
+    public static boolean finished;
+
+    public void backTrack(int[] solutionVec, int pos, int inputSize) {
+        int[] outCandidates = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+        int nCandidate;
+
+        if (isASolution(solutionVec, pos, inputSize)) {
+            processSolution(solutionVec, pos, inputSize);
+        } else {
+            pos += 1;
+
+            nCandidate = constructCandidates(solutionVec, pos, inputSize, outCandidates);
+
+            for (int i = 0; i < nCandidate; i++) {
+                solutionVec[pos] = outCandidates[i];
+
+                makeMove(solutionVec, pos, inputSize);
+                backTrack(solutionVec, pos, inputSize);
+                unmakeMove(solutionVec, pos, inputSize);
+
+                if (finished) // terminate early
+                    return;
+            }
+        }
+
+    }
+
+    protected abstract void unmakeMove(int[] solutionVec, int pos, int size);
+
+    protected abstract void makeMove(int[] solutionVec, int pos, int size);
+
+    protected abstract int constructCandidates(int[] solutionVec, int pos, int size, int[] outCandidates);
+
+    protected abstract void processSolution(int[] solutionVec, int pos, int inputSize);
+
+    protected abstract boolean isASolution(int[] solutionVec, int pos, int inputSize);
+}

src/main/java/org/sean/backtracking/Permutation.java

@@ -0,0 +1,56 @@
+package org.sean.backtracking;
+
+/**
+ * Created by Sean on 6/4/17.
+ */
+public class Permutation extends BackTrack {
+    public static void main(String[] args) {
+        int[] vec = new int[10];
+        new Permutation().backTrack(vec, 0, 3);
+    }
+
+    @Override
+    protected void unmakeMove(int[] solutionVec, int pos, int size) {
+
+    }
+
+    @Override
+    protected void makeMove(int[] solutionVec, int pos, int size) {
+
+    }
+
+    @Override
+    protected int constructCandidates(int[] solutionVec, int pos, int size, int[] outCandidates) {
+        int[] inPerm = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+        for (int i = 0; i < inPerm.length; i++) {
+            inPerm[i] = 0;
+        }
+
+        for (int j = 0; j < pos; j++) {
+            inPerm[solutionVec[j]] = 1;
+        }
+
+        int nCount = 0;
+        for (int i = 0; i <= size; i++) {
+            if (inPerm[i] == 0) {
+                outCandidates[nCount] = i;
+
+                nCount += 1;
+            }
+        }
+        return nCount;
+    }
+
+    @Override
+    protected void processSolution(int[] solutionVec, int pos, int inputSize) {
+        for (int i = 1; i <= pos; i++) {
+            System.out.print(String.format(" %d", solutionVec[i]));
+        }
+        System.out.println("");
+    }
+
+    @Override
+    protected boolean isASolution(int[] solutionVec, int pos, int inputSize) {
+        return pos == inputSize;
+    }
+}