Longest Common Subsequence in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the 2D array for dynamic programming.

DSA Typescript

const dp: number[][] = Array(m + 1).fill(null).map(() => Array([1]).fill(0));

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Am + 1

Bn + 1

Cn

Dm

Attempts:

3 left

💡 Hint

Common Mistakes

Using m instead of n for the inner array size.

Not adding 1 to the lengths for dp array size.

The dp array has dimensions (m+1) x (n+1) to cover all prefixes of both strings.

2fill in blank

medium

Complete the code to check if characters match at current indices.

DSA Typescript

if (text1[i - 1] [1] text2[j - 1]) {

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A==

B!=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using inequality instead of equality.

Using greater than or less than operators.

We check if characters at positions i-1 and j-1 are equal to extend the subsequence.

3fill in blank

hard

Fix the error in updating dp when characters do not match.

DSA Typescript

dp[i][j] = Math.max(dp[i - 1][j], dp[i][[1]]);

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Aj - 1

Bi - 1

Cj + 1

Di + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using i-1 instead of j-1 for the second index.

Using j+1 or i+1 which goes out of bounds.

When characters don't match, dp[i][j] is max of dp[i-1][j] and dp[i][j-1].

4fill in blank

hard

Fill both blanks to complete the nested loops iterating over dp table.

DSA Typescript

for (let i = 1; i [1] m + 1; i++) {
  for (let j = 1; j [2] n + 1; j++) {

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A<

B<=

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causes index out of bounds.

Using > or >= reverses loop logic.

Loops run from 1 up to but not including m+1 and n+1, so use '<' operator.

5fill in blank

hard

Fill all three blanks to return the final LCS length from dp table.

DSA Typescript

return dp[1][2][3];

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A[m]

B[n]

C[n][m]

D[m][n]

Attempts:

3 left

💡 Hint

Common Mistakes

Using dp[n][m] which swaps indices.

Using dp[m] or dp[n] which returns a row or column, not a single value.

The LCS length is stored at dp[m][n], the bottom-right cell of the dp table.