Count Occurrences of Element in Sorted Array in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find the first occurrence of the target in the sorted array.

DSA C++

int firstOccurrence(const vector<int>& nums, int target) {
    int left = 0, right = nums.size() - 1;
    int result = -1;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        if (nums[mid] == target) {
            result = mid;
            right = mid [1] 1;
        } else if (nums[mid] < target) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }
    return result;
}

Drag options to blanks, or click blank then click option'

A+

B/

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '-' causes infinite loop or wrong index.

Not updating right pointer after finding target.

When we find the target, we move the right pointer to mid - 1 to continue searching on the left side for the first occurrence.

2fill in blank

medium

Complete the code to find the last occurrence of the target in the sorted array.

DSA C++

int lastOccurrence(const vector<int>& nums, int target) {
    int left = 0, right = nums.size() - 1;
    int result = -1;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        if (nums[mid] == target) {
            result = mid;
            left = mid [1] 1;
        } else if (nums[mid] < target) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }
    return result;
}

Drag options to blanks, or click blank then click option'

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Moving right pointer instead of left after finding target.

Using '-' instead of '+' causing wrong search direction.

When the target is found, move the left pointer to mid + 1 to search the right side for the last occurrence.

3fill in blank

hard

Fix the error in the countOccurrences function to correctly calculate the count of target in the array.

DSA C++

int countOccurrences(const vector<int>& nums, int target) {
    int first = firstOccurrence(nums, target);
    if (first == -1) return 0;
    int last = lastOccurrence(nums, target);
    return last [1] first + 1;
}

Drag options to blanks, or click blank then click option'

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '-' causes incorrect count.

Forgetting to add 1 after subtraction.

The count is last index minus first index plus one, so use '-' between last and first.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps each word to its length only if the length is greater than 3.

DSA C++

auto result = std::unordered_map<std::string, int>{};
for (const auto& word : words) {
    if (word.size() [1] 3) {
        result[word] = word[2]size();
    }
}

Drag options to blanks, or click blank then click option'

A>

B<

C()

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causes wrong filtering.

Using '[]' instead of '()' to call size method.

We check if word size is greater than 3 using '>' and get size using '()' after word.

5fill in blank

hard

Fill all three blanks to create a map of uppercase words to their lengths only if length is greater than 4.

DSA C++

std::unordered_map<std::string, int> result;
for (const auto& word : words) {
    if (word.size() [1] 4) {
        std::string upper_word = word;
        std::transform(upper_word.begin(), upper_word.end(), upper_word.begin(), ::[2]);
        result[[3]] = word.size();
    }
}

Drag options to blanks, or click blank then click option'

A>

Btoupper

Cupper_word

Dtolower

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' for size comparison.

Using 'tolower' instead of 'toupper' for uppercase.

Using 'word' instead of 'upper_word' as map key.

We check if size is greater than 4, use 'toupper' to convert characters, and use 'upper_word' as the key in the map.