CS 2402
Spring 2009
Sample Code – Backtracking, Stacks and the Subset Sum Problem
public class subSetSum{
// Solving Subset sum using a stack
// Programmed by Fuentes, Feb. 9, 2009
// Subset sum consists of finding a subset of mySet whose elements add up to goal
// It is a well-known NP-complete problem
public static void main(String[] args) {
myStack S = new myStack();
int [] mySet ={2,5,8,9,12,21,33};
int lastItem =mySet.length-1;
int goal = 61;
int x, newItem;
S.push(0);
int sumStack = mySet[0];
boolean done = false;
System.out.println("The Goal is : "+goal);
while (!done) {
// Uncomment to debug, show stack contents and sum of stack elements
S.printSet(mySet);
System.out.println("Sum Stack "+sumStack);
if (sumStack == goal){
done = true;
System.out.println("The Solution is: ");
S.printSet(mySet);
}
else
if ((sumStack>goal)|(S.peek()==lastItem)){ //Backtrack
System.out.println("Backtracking ");
x = S.pop();
sumStack -= mySet[x];
if (x==lastItem){ // No more elements to add
if(S.isEmpty()){
done = true;
System.out.println("No Solution");
}
else{
x = S.pop();
sumStack -= mySet[x];
}
}
if (!done){
S.push(x+1);
sumStack += mySet[x+1];
}
}
else
if (S.peek()<lastItem){ // Add more elements to stack
System.out.println("Adding more elements ");
