Recursive code gives wrong answer in Javascript

Question

I want to print all subsets of an array using backtracking in Javascript my algorithm is right but it gives some unexpected answers. I think this is related to javascript language.

// this is base function where i am calling recursive function .
function solveIt(A,B,C,D,E){
      let ans = [];   // this is ans array
      let sub = [];    // this is subset array 
      printAllSubset(A,0,sub,ans); // Calling the helper function
      return ans;    // returing anser
       
    
}

// My recursive code 
function printAllSubset(nums,idx,sub,ans){
    
    if(idx==nums.length){.   // This is base condition
        ans.push(sub);
       
        return ans;
        
    }
    // include current index
    sub.push(nums[idx]);            // including the current index
    printAllSubset(nums,idx+1,sub,ans);  // recuring for all possible sub problem
    
    // exclude current index
    
    sub.pop();                            // excluding the current index
    printAllSubset(nums,idx+1,sub,ans);   // recuring for all possible scenerio
     
    
}

const A=[1,2,3];
const res = solveIt(A,B,C);

console.log(res)

// output I am getting - 
[
  [], [], [], [],
  [], [], [], []
]

// But the expected output should be - 

[[],[1],[2],[1,2],[3],[1,3],[2,3],[1,2,3]]

Answer 1

You build towards having the answer in ans but then throw it away. One answer is to make ans a global variable and remove it from recursive function calls:

let ans=[]
function solveIt(A){ 
      printAllSubset(A,0,[]); // Calling the helper function
}

function printAllSubset(nums,idx,sub){

    if(idx===nums.length){.   // This is base condition
        ans.push(sub);
    }
    // include current index
    sub.push(nums[idx]);            // including the     current index
    printAllSubset(nums,idx+1,sub);  // recuring for all possible sub problem

    // exclude current index

    sub.pop();                            // excluding the current index
    printAllSubset(nums,idx+1,sub);   // recuring for all possible scenerio
}

The other is to catch the return of the recursive calls to printAllSubset:

function solveIt(A){ 
      return printAllSubset(A,0,[],[]); // Calling the helper function
}

function printAllSubset(nums,idx,sub,ans){

    if(idx===nums.length){.   // This is base condition
        ans.push(sub);
   
        return ans;
    
    }
    // include current index
    sub.push(nums[idx]);            // including the     current index
    ans=printAllSubset(nums,idx+1,sub,ans);  // recuring for all possible sub problem

    // exclude current index

    sub.pop();                            // excluding the current index
    ans=printAllSubset(nums,idx+1,sub,ans);   // recuring for all possible scenerio

    return ans;
}