Generate All Combinations Sum K in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the backtracking with an empty combination.

DSA Typescript

function combinationSumK(k: number, n: number): number[][] {
  const result: number[][] = [];
  function backtrack(start: number, comb: number[], sum: number) {
    // backtracking logic here
  }
  backtrack([1], [], 0);
  return result;
}

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An

B0

Ck

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from 0 instead of 1 causes invalid combinations.

Starting from k or n misses smaller numbers.

We start from number 1 because the problem uses numbers 1 to 9 for combinations.

2fill in blank

medium

Complete the condition to stop backtracking when the combination size reaches k.

DSA Typescript

function backtrack(start: number, comb: number[], sum: number) {
  if (comb.length === [1]) {
    if (sum === n) {
      result.push([...comb]);
    }
    return;
  }
  // continue backtracking
}

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Ak

Bn

Csum

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing length to n instead of k.

Using sum instead of length for stopping condition.

We stop when the combination length equals k, the required size.

3fill in blank

hard

Fix the error in the for-loop range to avoid invalid numbers.

DSA Typescript

for (let i = start; i <= [1]; i++) {
  if (sum + i > n) break;
  comb.push(i);
  backtrack(i + 1, comb, sum + i);
  comb.pop();
}

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A9

Bk

Cn

Dsum

Attempts:

3 left

💡 Hint

Common Mistakes

Looping up to n or k causes out-of-range numbers.

Using sum as loop limit causes errors.

Numbers 1 to 9 are allowed, so loop must go up to 9.

4fill in blank

hard

Fill both blanks to correctly add and remove numbers during backtracking.

DSA Typescript

comb.[1](i);
backtrack(i + 1, comb, sum + i);
comb.[2]();

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Apush

Bpop

Cshift

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using shift or unshift changes the wrong end of the array.

Not removing elements causes incorrect combinations.

Use push to add and pop to remove the last element for backtracking.

5fill in blank

hard

Fill all three blanks to complete the backtracking function signature and call.

DSA Typescript

function backtrack([1]: number, [2]: number[], [3]: number) {
  // backtracking logic
}
backtrack(1, [], 0);

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Astart

Bcomb

Csum

Dindex

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter names causes confusion.

Mixing types or order breaks the function.

The function uses start (number), comb (array), and sum (number) as parameters.