Backtracking Concept and Decision Tree Visualization in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the backtracking recursion from the first position.

DSA C

void solve() {
    int start = [1];
    backtrack(start);
}

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ANULL

B1

C-1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from 1 instead of 0

Using NULL for an integer index

The backtracking usually starts from index 0 to cover all possibilities from the beginning.

2fill in blank

medium

Complete the code to check if the current choice is valid before proceeding.

DSA C

if (isValid([1])) {
    backtrack(pos + 1);
}

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A0

Bpos + 1

Cpos

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Passing pos + 1 instead of pos

Passing NULL or 0 incorrectly

We check if the current position choice is valid before moving forward.

3fill in blank

hard

Fix the error in the backtracking base case to stop recursion correctly.

DSA C

if (pos == [1]) {
    printSolution();
    return;
}

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An

B0

C-1

Dpos

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or -1 as base case

Using pos instead of n

The base case is when the position reaches n, meaning all positions are processed.

4fill in blank

hard

Fill both blanks to correctly undo the choice after backtracking.

DSA C

choices[pos] = [1];
backtrack(pos + 1);
choices[pos] = [2];

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Atrue

Bfalse

C0

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Not undoing the choice

Using 0 and -1 inconsistently

We mark the choice as made (true), recurse, then undo it (false) to explore other options.

5fill in blank

hard

Fill all three blanks to build a decision tree node and recurse correctly.

DSA C

struct Node {
    int choice;
    struct Node* [1];
    struct Node* [2];
};

void explore(struct Node* node) {
    if (node == NULL) return;
    process(node->choice);
    explore(node->[3]);
}

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Aleft

Bright

Cchild

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using child or next instead of left/right

Recursing on right instead of left

The decision tree node has left and right children. We recurse on the left child in explore.