Search in 2D Matrix in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return true if the target is found in the matrix.

DSA C++

bool searchMatrix(vector<vector<int>>& matrix, int target) {
    for (int i = 0; i < matrix.size(); i++) {
        for (int j = 0; j < matrix[0].size(); j++) {
            if (matrix[i][j] == [1]) {
                return true;
            }
        }
    }
    return false;
}

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Atarget

Bi

Cj

Dmatrix

Attempts:

3 left

💡 Hint

Common Mistakes

Using loop indices instead of the target value for comparison.

Comparing with the entire matrix instead of a single element.

We compare each element matrix[i][j] with the target value to find a match.

2fill in blank

medium

Complete the code to perform binary search on a sorted row to find the target.

DSA C++

bool binarySearchRow(vector<int>& row, int target) {
    int left = 0, right = row.size() - 1;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        if (row[mid] == [1]) {
            return true;
        } else if (row[mid] < target) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }
    return false;
}

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Atarget

Bleft

Cmid

Dright

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with indices instead of the target value.

Using wrong variable names for comparison.

We compare the middle element row[mid] with the target value to check for equality.

3fill in blank

hard

Fix the error in the code to correctly search the matrix using binary search on rows.

DSA C++

bool searchMatrix(vector<vector<int>>& matrix, int target) {
    int top = 0, bottom = matrix.size() - 1;
    while (top <= bottom) {
        int mid = top + (bottom - top) / 2;
        if (matrix[mid][0] == [1]) {
            return true;
        } else if (matrix[mid][0] < target) {
            top = mid + 1;
        } else {
            bottom = mid - 1;
        }
    }
    return false;
}

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Amid

Btarget

Ctop

Dbottom

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with mid index instead of target value.

Using wrong variable for comparison.

We compare the first element of the middle row with the target to decide which half to search next.

4fill in blank

hard

Fill both blanks to complete the code that finds the correct row and then searches it.

DSA C++

bool searchMatrix(vector<vector<int>>& matrix, int target) {
    int top = 0, bottom = matrix.size() - 1;
    while (top <= bottom) {
        int mid = top + (bottom - top) / 2;
        if (matrix[mid][0] == target) {
            return true;
        } else if (matrix[mid][0] [1] target) {
            top = mid + 1;
        } else {
            bottom = mid - 1;
        }
    }
    int row = bottom;
    if (row < 0) return false;
    return binarySearchRow(matrix[row], [2]);
}

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A<

B>

Ctarget

Drow

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operator.

Passing wrong argument to binary search.

We check if the first element of mid row is less than target to move top pointer. Then we search the found row for the target.

5fill in blank

hard

Fill all three blanks to complete the optimized search in 2D matrix.

DSA C++

bool searchMatrix(vector<vector<int>>& matrix, int target) {
    if (matrix.empty() || matrix[0].empty()) return false;
    int rows = matrix.size(), cols = matrix[0].size();
    int left = 0, right = rows * cols - 1;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        int mid_value = matrix[mid / [1]][mid % [2]];
        if (mid_value == [3]) {
            return true;
        } else if (mid_value < target) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }
    return false;
}

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Acols

Brows

Ctarget

Dleft

Attempts:

3 left

💡 Hint

Common Mistakes

Using rows instead of cols for index calculations.

Comparing with wrong variable.

We use 'cols' to convert 1D mid index to 2D indices. We compare mid_value with target to decide search direction.