Question

I am relatively new to programming. As the title suggests I require an algorithm that lets me get the same function of a variable nested loop. i.e.

for(..)
{ for(..){
for(..){....}
.
.
}}

The Number of nested loop will vary depending upon user input. What I am trying to achieve is finding all combinations of the numbers (10,9,8,7,6,5,4) Now I have read many. Either I dont understand them fully (I am new to programming world) or It doesnt serve my purpose. I need these combinations later in certain calculations and not just print all the combinations. One way, as I have learnt is to use recursion. I dont understand it fully. I tried to make a recursive function but failed miserably. This is what I want

10 10 10 
10 10 9
10 10 8
.
.
.
4  4  4 

The number can change (like 10 10 10 10 , 10 10 10 9 .. ) These combinations are to be stored in an array as I need them to manipulate later. Please keep it simple and comment.

Preferred language will be java. Any Language will do. A general algorithm is highly recommended. P.S. This is not a homework.

Thanks to amit. Here is the working code

def findcombinations(array,n,sol,tt=[]):
    if (n== 0):
        tt.append(sol[:])
        return
    for x in array:
        sol.append(x)
        findcombinations(array,n-1,sol,tt)        
        del sol[-1]
    return tt      

To call the function use
print(findcombinations([1,2],3,[]))

Answer 1

Usually when you need “dynamic loops” – it is a strong indication you actually need recursion.

For example, finding all possible combinations of size n of digits in array [pseudo code]:

findCombinations(array,n,sol):
   if (sol.size == n): //stop condition for the recursion
      print sol
      return
   for each x in array:
      sol.append(x)
      findCombinations(array,n-1,sol) //recursive call
      sol.removeLast() //cleaning up environment

The above pseudo-code will find and print all sequences of length n made from elements from array [each element can appear more then once]