Search in 2D Matrix in DSA Typescript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of the search function?

Given the matrix and the target, what will the search function return?

DSA Typescript

function searchMatrix(matrix: number[][], target: number): boolean {
  let row = 0;
  let col = matrix[0].length - 1;
  while (row < matrix.length && col >= 0) {
    if (matrix[row][col] === target) {
      return true;
    } else if (matrix[row][col] > target) {
      col--;
    } else {
      row++;
    }
  }
  return false;
}

const matrix = [
  [1, 4, 7, 11],
  [2, 5, 8, 12],
  [3, 6, 9, 16],
  [10, 13, 14, 17]
];
const target = 5;
console.log(searchMatrix(matrix, target));

A true

B false

C undefined

D TypeError

💡 Hint

Start from top-right corner and move left or down based on comparison.

The function starts at top-right (11), since 11 > 5, it moves left to 7, then 4, then moves down to 5 which matches the target, so returns true.

❓ Predict Output

intermediate

What is the output of the search for a missing target?

What will the function return when searching for a target not in the matrix?

DSA Typescript

function searchMatrix(matrix: number[][], target: number): boolean {
  let row = 0;
  let col = matrix[0].length - 1;
  while (row < matrix.length && col >= 0) {
    if (matrix[row][col] === target) {
      return true;
    } else if (matrix[row][col] > target) {
      col--;
    } else {
      row++;
    }
  }
  return false;
}

const matrix = [
  [1, 4, 7, 11],
  [2, 5, 8, 12],
  [3, 6, 9, 16],
  [10, 13, 14, 17]
];
const target = 15;
console.log(searchMatrix(matrix, target));

A undefined

B RangeError

C false

D true

💡 Hint

If the target is not found, the function returns false.

The function moves through the matrix but never finds 15, so it returns false.

🧠 Conceptual

advanced

Why does the search start from the top-right corner?

Why is the top-right corner chosen as the starting point for searching in a sorted 2D matrix?

A Because top-right corner is always the smallest element in the matrix.

B Because it is easier to implement recursion from top-right corner.

C Because starting from top-right allows binary search on rows only.

D Because from top-right, we can move left to smaller numbers and down to larger numbers, narrowing search efficiently.

💡 Hint

Think about how the matrix is sorted and how moving left or down changes values.

The matrix rows and columns are sorted ascending. From top-right, moving left decreases values, moving down increases values, allowing efficient elimination of rows or columns.

🔧 Debug

advanced

What error does this code produce?

What error will this code produce when run?

DSA Typescript

function searchMatrix(matrix: number[][], target: number): boolean {
  let row = 0;
  let col = matrix[0].length;
  while (row < matrix.length && col >= 0) {
    if (matrix[row][col] === target) {
      return true;
    } else if (matrix[row][col] > target) {
      col--;
    } else {
      row++;
    }
  }
  return false;
}

const matrix = [
  [1, 4, 7, 11],
  [2, 5, 8, 12],
  [3, 6, 9, 16],
  [10, 13, 14, 17]
];
const target = 5;
console.log(searchMatrix(matrix, target));

A IndexError

B RangeError

C TypeError

D undefined behavior

💡 Hint

Check the initial value of col and array indexing.

col is initialized to matrix[0].length which is out of bounds (indexing starts at 0), so accessing matrix[row][col] causes RangeError.

🚀 Application

expert

How many elements are checked in worst case?

Given an n x n matrix sorted as described, what is the maximum number of elements the search function checks in the worst case?

A 2n

B log n

C n^2

D n

💡 Hint

Consider the path the search pointer takes from top-right to bottom-left.

The search moves at most n steps down and n steps left, so maximum 2n elements are checked.