LeetCode Challenge: 48. Rotate Image - JavaScript Solution 🚀

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The Rotate Image problem involves rotating an n×n matrix by 90 degrees clockwise, in place. Let’s solve LeetCode 48: Rotate Image step by step.

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🚀 Problem Description

Given an n×n matrix:

• Rotate the matrix in place by 90 degrees clockwise.
• In-place means modifying the original matrix without allocating extra space for another matrix.

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💡 Examples

Example 1

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

Example 2

Input: matrix = [[5, 1, 9, 11], [2, 4, 8, 10], [13, 3, 6, 7], [15, 14, 12, 16]]  
Output: [[15, 13, 2, 5], [14, 3, 4, 1], [12, 6, 8, 9], [16, 7, 10, 11]]

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Constraints

• 1≤m,n≤10
• −100≤matrix[i][j]≤100

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🏆 JavaScript Solution

We solve this problem in two steps:

1. Transpose the Matrix:

   • Swap elements symmetrically across the diagonal.

2. Reverse Each Row:

   • Reverse the order of elements in each row to achieve the rotation.

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Implementation

var rotate = function(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();
    }
};

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🔍 How It Works

1. Transpose the Matrix:
   • Swap matrix[i][j] with matrix[j][i] for all i<j.
   • This converts rows into columns.

Example:

Input:  [[1, 2, 3],       Transposed:  [[1, 4, 7],  
         [4, 5, 6],  ->                [2, 5, 8],  
         [7, 8, 9]]                    [3, 6, 9]]

1. Reverse Each Row:
   • Reverse the elements of each row to achieve the clockwise rotation.

Example:

Transposed: [[1, 4, 7],       Rotated: [[7, 4, 1],  
             [2, 5, 8],  ->            [8, 5, 2],  
             [3, 6, 9]]                [9, 6, 3]]

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🔑 Complexity Analysis

• Time Complexity:

  • Transposing the matrix takes O(n^2).
  • Reversing each row takes O(n^2).
  • Total: O(n^2)

• Space Complexity: O(1), as the rotation is done in place.

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📋 Dry Run

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

Output: [[7, 4, 1], [8, 5, 2], [9, 6, 3]]

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✨ Pro Tips for Interviews

1. Clarify Constraints:

   • Ensure the matrix is always square (n×n).

2. Highlight In-Place Operations:

   • Emphasize the efficiency of the transpose-and-reverse method.

3. Edge Cases:

   • Single-element matrix: [[1]].
   • 2×2 matrix: [[1, 2], [3, 4]].

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📚 Learn More

Check out the full explanation and code walkthrough on my previous Dev.to post:
👉 Spiral Matrix - JavaScript Solution

What’s your preferred method to solve this problem? Let’s discuss! 🚀

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Comments

[Rahul Kumar Barnwal]

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