How to write a function using recursion that takes 2 integers and returns an array containing intege-CodePudding

I'm trying to write a function that will take 2 integers as variables startNum and endNum and return an array containing all the integers in between the 2 variables.

So for example if we input (3,6) we should get as a return an array [3,4,5,6]. For this problem we assume that startNum will always be smaller than EndNum. Also if startNum and endNum are the same, the function should still work.

I've written the following code but i get an error in the console.

function rangeOfNumbers(startNum, endNum) {
  
  return startNum === 0 && endNum === 0 ?[]: [startNum,rangeOfNumbers(startNum   1),...endNum];
  
}

I get this error message: RangeError: Maximum call stack size exceeded.
Can anyone tell me why it's not working?

CodePudding user response：

A simple enough change should make the recursive approach work, we keep on calling recursively until the startNum is greater than the endNum.

function rangeOfNumbers(startNum, endNum) {
    return startNum > endNum ? [] : [startNum, ...rangeOfNumbers(startNum   1, endNum)];
} 

console.log(JSON.stringify(rangeOfNumbers(1, 5)));
console.log(JSON.stringify(rangeOfNumbers(2, 2)));

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Also, here's a simple way to generate a number range using Array.from().

We generate the resulting array, first by specifying the length, then using the key passed to the populating callback to create the actual contents.

function rangeOfNumbers(startNum, endNum) {
    return Array.from( { length: (endNum - startNum   1) }, (v,k) => startNum   k); 
} 

console.log(JSON.stringify(rangeOfNumbers(1, 5)));

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CodePudding user response：

 function rangeOfNumbers(startNum, endNum)
    { 
      //Add this condition for avoid stack issue
      if(startNum >=endNum) 
          return [];
      if (endNum - startNum === 2)
         return [startNum   1];
      
      let list = rangeOfNumbers(startNum, endNum - 1);
      list.push(endNum - 1);
      return list;
    };

CodePudding user response：

Small change in your function to check if startNum is greater than endNum, return empty array and increment startNum at every recursion call.

function rangeOfNumbers(startNum, endNum) {
  if (startNum > endNum) {
    return [];
  }
  return [startNum, ...rangeOfNumbers(startNum   1, endNum)];  
}

console.log(rangeOfNumbers(3, 6));

CodePudding user response：

function rangeOfNumbers(startNum, endNum) {
    if (startNum == endNum) {
        return [startNum] // Base case
    }
    return [startNum, ...rangeOfNumbers(startNum   1, endNum)]
}

console.log(JSON.stringify(rangeOfNumbers(3, 6)));

A helpful tip is to figure out what the base case and the subtask are.

In this case, the base case is the situation where startNum == endNum. A one-element list should be returned.

As for the subtask, you may decompose the task like this:

rangeOfNumbers(3, 6)
= [3, ...rangeOfNumbers(4, 6)]
= [3, ...[4, ...rangeOfNumbers(5, 6)]]
//... and so on

CodePudding user response：

You don't need recursion to achieve that. You can do it like this:

function rangeOfNumbers(start, end) {
    var result = [];
    for (let i = start; i <= end; i  ) {
        result.push(i);
    }
    return result;
}

console.log(rangeOfNumbers(4,8)); // Outputs: [4, 5, 6, 7, 8]