Rotate Matrix By 90 Degree

Rotate given matrix by 90 degree but rotation must be in place rotation

Conditions:

• In place rotation
• 2 D matrix
• And clockwise rotation

Solution:

• We’ll rotate layer by layer
• Total number layer required to rotate = n / 2
• We will swap following cells values for every layer rotation:
  • TopLeft -> TopRight
  • TopRight – BottomRight
  • BottomRight -> BottomLeft
  • BottomLeft -> TopRight
• Cells
  • TopLeft = layer, layer
  • TopRight = n – layer – 1, layer
  • BottomLeft = layer, n – layer – 1
  • BottomRight = n – layer – 1, n – layer – 1

Algorithm:

1. First check matrix is square or not
   1. Iterate layer from 0 to n/2
      1. Set FirstCell = rotation
      2. Set LastCell = n – layer – 1
      3. Iterate cell from FirstCell to LastCell
         1. Set offset = i – FirstCell
         2. Set topLeftValue = matrix[FirstCell][i]
         3. Set matrix[FirstCell][i] = matrix [last-offset][FirstCell]
         4. Set matrix [LastCell – offset][FirstCell] = matrix [last-offset] [LastCell]
         5. Set matrix [LastCell – offset][LastCell] = matrix [i][LastCell]
         6. Set matrix [i][LastCell] = topLeftValue

Video

Latest Source Code:
Github: RotateMatrixBy90Degree.java

Output:

7 4 1 
8 5 2 
9 6 3