48. Rotate Image

Link

Solution

matrix rotate method overview

clock wise:

1st step : Reverse all row, swap(matrix[i], matrix[n-1-i] for all i = 0 ~ n/2

1 2 3 7 8 9 4 5 6 -> 4 5 6 7 8 9 1 2 3

2nd step : swap(matrix[i][j] , matrix[j][i]) for i = 0->n-1, for j = i+1 -> n-1

7 8 9 7 4 1 4 5 6 -> 8 5 2 1 2 3 9 6 3

public void rotate(int[][] matrix) {
       //reverse matix row
        int n = matrix.length;
        for(int i = 0; i < n/2; i++){
            //swap all element in matrix[i] to matrix[n-i]
            int[] temp = matrix[i];
            matrix[i] = matrix[n-1-i];
            matrix[n-1-i] = temp;
        }
        
        //swap matrix[i][j], matrix[j][i] for all i != j
        for(int i = 0; i < n; i++){
            //j = i+1 is crucial to let the swap not duplicated
            for(int j = i+1; j < n; j++){
                int temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
    }

Anti-clock wise:

1st step : Reverse all element in the raw

1 2 3 3 2 1 4 5 6 -> 6 5 4 7 8 9 9 8 7

2nd step : swap(matrix[i][j] , matrix[j][i]) for i = 0->n-1, for j = i+1 -> n-1

3 2 1 3 6 9 6 5 4 -> 2 5 8 9 8 7 1 4 7

    public void rotate(int[][] matrix) {
       //reverse matix colum
        int n = matrix.length;
        for(int i = 0; i < n; i++){
            //swap all element in matrix[i] to matrix[n-i]
            for(int j = 0; j < n/2; j++){
                int temp = matrix[i][j];
                matrix[i][j] = matrix[i][n-1-j];
                matrix[i][n-1-j] = temp;
            }
            
        }
        
        //swap matrix[i][j], matrix[j][i] for all i != j
        for(int i = 0; i < n; i++){
            //j = i+1 is crucial to let the swap not duplicated
            for(int j = i+1; j < n; j++){
                int temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
    }