3
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Please review performance

https://leetcode.com/problems/transpose-matrix/

Given a matrix A, return the transpose of A.

The transpose of a matrix is the matrix flipped over it's main diagonal, switching the row and column indices of the matrix.

Example 1:

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

Example 2:

Input: [[1,2,3],[4,5,6]] Output: [[1,4],[2,5],[3,6]]

Note:

1 <= A.length <= 1000 1 <= A[0].length <= 1000

using System;
using System.Linq;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace ArrayQuestions
{
    [TestClass]
    public class TransposeMatrix
    {

        /// <summary>
        /// 1 2 3       1 4 7
        /// 4 5 6       2 5 8
        /// 7 8 9       3 6 9
        /// </summary>
        [TestMethod]
        public void Transpose3X3()
        {
            int[][] matrix = { new[] { 1, 2, 3 }, new[] { 4, 5, 6 }, new[] { 7, 8, 9 } };
            int[][] expected = { new[] { 1, 4, 7 }, new[] { 2, 5, 8 }, new[] { 3, 6, 9 } };
            int[][] output = Transpose(matrix);
            for (int i = 0; i < output.GetLength(0); i++)
            {
                CollectionAssert.AreEqual(expected[i], output[i]);
            }
        }

        [TestMethod]
        public void Transpose2X3()
        {
            int[][] matrix = { new[] { 1, 2, 3 }, new[] { 4, 5, 6 } };
            int[][] expected = { new[] { 1, 4 }, new[] { 2, 5 }, new[] { 3, 6} };
            int[][] output = Transpose(matrix);
            for (int i = 0; i < output.GetLength(0); i++)
            {
                CollectionAssert.AreEqual(expected[i], output[i]);
            }
        }
        public int[][] Transpose(int[][] A)
        {
            int h = A.GetLength(0);
            int w = A[0].GetLength(0);

            //we need to allocate the matrix as transposed already
            //for example 2x3 should allocate 3x2
            int[][] res = new int[w][];
            for (int i = 0; i < w; i++)
            {
                res[i] = new int[h];
            }

            for (int r = 0; r < h; r++)
            {
                for (int c = 0; c < w; c++)
                {
                    res[c][r] = A[r][c];
                }
            }
            return res;
        }
    }
}
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6
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You iterate through the same array twice (once while initializing and once while assigning values), you can do both inside the same loop.

for (int i = 0; i < w; i++)
{
    res[i] = new int[h];
    for (int j = 0; j < h; j++)
    {
        res[i][j] = A[j][i];
    }
}
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