Saturday, April 4, 2015

LeetCode [48] Rotate Image

You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).
Note:
You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.
Example 1:
Given input matrix = 
[
  [1,2,3],
  [4,5,6],
  [7,8,9]
],

rotate the input matrix in-place such that it becomes:
[
  [7,4,1],
  [8,5,2],
  [9,6,3]
]
Example 2:
Given input matrix =
[
  [ 5, 1, 9,11],
  [ 2, 4, 8,10],
  [13, 3, 6, 7],
  [15,14,12,16]
], 

rotate the input matrix in-place such that it becomes:
[
  [15,13, 2, 5],
  [14, 3, 4, 1],
  [12, 6, 8, 9],
  [16, 7,10,11]
]
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class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int n = matrix.size();
        for(int i = 0; i<=(n-1)/2; ++i){//layers from out-most to inner-most
            for(int j = i; j<n-1-i; ++j){
                int top = matrix[i][j];
                matrix[i][j] = matrix[n-1-j][i];//left -> top
                matrix[n-1-j][i] = matrix[n-1-i][n-1-j];//bottom -> left
                matrix[n-1-i][n-1-j] = matrix[j][n-1-i];//right -> bottom;
                matrix[j][n-1-i] = top;//top -> right;
            }
        }
    }
};

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 class Solution {
    public void rotate(int[][] matrix) {
        int n = matrix.length;
        int layers = n/2;
        
        for(int l = 0; l<layers; ++l){
            int sz =n-2*l-1;
            for(int offset = 0; offset<sz; ++offset){
                int tmp = matrix[l][l+offset];
                
                //left to top
                matrix[l][l+offset] = matrix[n-1-l-offset][l];
                
                //bottom to left
                matrix[n-1-l-offset][l] = matrix[n-1-l][n-1-l-offset];
                
                //right to left;
                matrix[n-1-l][n-1-l-offset] = matrix[l+offset][n-1-l];
                
                //top to right
                matrix[l+offset][n-1-l] = tmp;
                
            //    print(matrix);
            }
        }
    }
    
    void print(int[][] matrix){
        for(int[] r : matrix) System.out.println(Arrays.toString(r));
        System.out.println("===========");
    }
}

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