Question

I’m sure I’m making a rookie mistake with java(this is actually my first program). I am trying to port some working python code I made into java(as a learning/testing exercise to learn a bit of the differences) but I’m getting different results between the two.

My program takes a list of data and generates another list based on it(basically sees if a value can be broken down by a sum). Python correctly gives 2,578 results while Java only gives 12. I tried to find the same commands in java and thought I did but can’t seem to figure out why the results differ(the difference between the two I have experienced problems with multi threading and syncing of variables, wasn’t sure if Java was doing anything behind the scenes so I had a while loop to keep running until the results stabilize, but it didn’t help). Any suggestions would be helpful.

Here’s the offending code(java at the top, python and pseudo code commented out in the bottom as reference):

                        for (int c = 0; c <= max_value; c++){
                            String temp_result = (s - c  * data.get(i) +  "," + i);

                            if( results.contains( temp_result ) ){  
                                String result_to_add = (s + "," + i+1);
                                if( results.contains( result_to_add ) ){ 
                                    System.out.println("contains result already");
                                } else {
                                    results.add(result_to_add);

                                }    print len(T)

#Here's the basic pseudo code(I added a few control variables but here's a high level view):

for i = 1 to k
    for z = 0 to sum:
        for c = 1 to z / x_i:
            if T[z - c * x_i][i - 1] is true:
                set T[z][i] to true
*/

Answer 1

In java s + "," + i+1 is a String concatenation : “10” + “,” + 4 + 1 will return 10,41.

Use String result_to_add = s + "," + (i+1); instead.