Binary Search on Answer Technique in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the search range for binary search on answer.

DSA C++

int low = 0;
int high = [1];

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

A100

B1000

C10

D1e9

Attempts:

3 left

💡 Hint

Common Mistakes

Setting high too low and missing the correct answer.

Using a small fixed number like 10 or 100 without reasoning.

The high value is set to a large number (1e9) to cover the maximum possible answer range.

2fill in blank

medium

Complete the code to calculate the middle value in binary search on answer.

DSA C++

int mid = low + ([1] - low) / 2;

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

Ahigh

Blow

Cmid

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using (low + high) / 2 directly which can overflow.

Using low instead of high in the calculation.

We calculate mid as low + (high - low) / 2 to avoid overflow.

3fill in blank

hard

Fix the error in the condition to update the search range based on feasibility check.

DSA C++

if (isPossible([1])) {
    high = mid - 1;
} else {
    low = mid + 1;
}

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

Amid

Blow

Chigh

Dmid + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Passing low or high instead of mid to isPossible.

Using mid + 1 which is not the current candidate.

The feasibility check should be done on mid, the current candidate answer.

4fill in blank

hard

Fill both blanks to complete the binary search loop condition and update low when answer is not possible.

DSA C++

while ([1] <= [2]) {
    int mid = low + (high - low) / 2;
    if (isPossible(mid)) {
        high = mid - 1;
    } else {
        low = mid + 1;
    }
}

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

Alow

Bhigh

Cmid

Dlow + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using mid in the while condition.

Using low + 1 in the while condition instead of high.

The loop continues while low is less than or equal to high.

We update low to mid + 1 when the answer is not possible.

5fill in blank

hard

Fill all three blanks to return the final answer after binary search on answer completes.

DSA C++

int binarySearchAnswer() {
    int low = 0, high = 1e9;
    int result = -1;
    while (low <= high) {
        int mid = low + (high - low) / 2;
        if (isPossible(mid)) {
            result = [1];
            high = [2];
        } else {
            low = [3];
        }
    }
    return result;
}

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

Amid

Bmid - 1

Cmid + 1

Dhigh

Attempts:

3 left

💡 Hint

Common Mistakes

Not updating result when mid is possible.

Incorrectly updating high or low boundaries.

When mid is possible, we store it in result and move high to mid - 1 to find a smaller possible answer.

Otherwise, we move low to mid + 1 to search higher.