Four Sum Problem All Unique Quadruplets in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to sort the array before processing.

DSA C

qsort(nums, numsSize, sizeof(int), [1]);

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AcompareInts

Bcmp

CcompareFunc

Dcompare

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong comparator function name.

Passing NULL instead of a comparator.

The qsort function requires a comparison function pointer. 'compareInts' is the correct comparator for integers.

2fill in blank

medium

Complete the code to skip duplicate elements in the first loop.

DSA C

for (int i = 0; i < numsSize - 3; i++) {
    if (i > 0 && nums[i] == nums[[1]]) continue;

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Ai + 1

Bi

Ci - 1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with i+1 which is the next element.

Comparing with i itself causing no skip.

To skip duplicates, compare current element with the previous one at index i-1.

3fill in blank

hard

Fix the error in the while loop condition to avoid infinite loops.

DSA C

while (left < right && nums[left] == nums[[1]]) left++;

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Aright

Bleft + 1

Cleft - 1

Dright - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with left+1 which may cause out-of-bound errors.

Comparing with left-1 which is invalid when left is 0.

We compare nums[left] with nums[right] to skip duplicates after finding a quadruplet.

4fill in blank

hard

Fill both blanks to correctly update pointers after finding a quadruplet.

DSA C

quadruplets[quadrupletCount][0] = nums[i];
quadruplets[quadrupletCount][1] = nums[j];
quadruplets[quadrupletCount][2] = nums[left];
quadruplets[quadrupletCount][3] = nums[right];
quadrupletCount++;
while (left < right && nums[left] == nums[left [1]]) left++;
while (left < right && nums[right] == nums[right [2]]) right--;

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A+1

B-1

C+2

D-2

Attempts:

3 left

💡 Hint

Common Mistakes

Using -1 for left pointer which moves it backward incorrectly.

Using +1 for right pointer which moves it forward incorrectly.

After adding a quadruplet, move left pointer forward by 1 and right pointer backward by 1 to skip duplicates.

5fill in blank

hard

Fill all three blanks to complete the condition checking if the sum matches the target.

DSA C

int sum = nums[i] + nums[j] + nums[left] + nums[right];
if (sum [1] target) {
    left++;
} else if (sum [2] target) {
    right--;
} else if (sum == target) {
    // add quadruplet
    [3];
}

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A<

B>

Csum = target

D/* add quadruplet code here */

Attempts:

3 left

💡 Hint

Common Mistakes

Using assignment '=' instead of comparison operators.

Not moving pointers correctly based on sum comparison.

If sum is less than target, move left pointer forward; if greater, move right pointer backward; if equal, add quadruplet.