Rotate an n x n 2D matrix 90 degrees clockwise in-place.

Example 1:

• Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
• Output: [[7,4,1],[8,5,2],[9,6,3]]

Constraints:

• n == matrix.length
• 1 <= n <= 20

Transpose matrix (swap matrix[i][j] with matrix[j][i]), then reverse each row.

Transpose + Reverse Rows

graph TD
    Start["Input Data"] --> Process["Process Element by Element"]
    Process --> Lookup{"Hash Map / Set Lookup"}
    Lookup -- "Match Found" --> Return["Return Indices / Result"]
    Lookup -- "No Match" --> Store["Store in Map / Set"]
    Store --> Process

function rotate(matrix) {
  const n = matrix.length;
  for (let i = 0; i < n; i++) {
    for (let j = i + 1; j < n; j++) {
      [matrix[i][j], matrix[j][i]] = [matrix[j][i], matrix[i][j]];
    }
  }
  for (let i = 0; i < n; i++) matrix[i].reverse();
  return matrix;
}

• Time Complexity: O(n^2)
• Space Complexity: O(1)
• Explanation: In-place transpose and row reverse.

function rotate(matrix) {
  const n = matrix.length;
  for (let i = 0; i < n; i++) {
    for (let j = i + 1; j < n; j++) {
      [matrix[i][j], matrix[j][i]] = [matrix[j][i], matrix[i][j]];
    }
  }
  for (let i = 0; i < n; i++) matrix[i].reverse();
  return matrix;
}

• Time Complexity: O(n^2)
• Space Complexity: O(1)
• Explanation: Transpose matrix diagonally, then flip rows horizontally.

1. Initialize State: Setup necessary pointers, dynamic programming arrays, or hash maps.
2. Iterate & Evaluate: Process the input according to the boundary conditions.
3. Update & Return: Compute the optimal answer and return early or at termination.

Rotate 90 deg clockwise = Transpose matrix + Reverse rows.

1. Transpose then reverse each row.

👉 Solve this problem interactively in the DSA Lab