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Leetcode-Rotate Image
You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).
Follow up:
Could you do this in-place?
Have you met this question in a real interview?
Analysis:
We can rotate the outest circle of the matrix, and then move to the next inner circle. I used a recursive method.
Solution:
1 public class Solution { 2 public void rotate(int[][] matrix) { 3 int len = matrix.length; 4 rotateRecur(matrix,0,0,len); 5 6 } 7 8 public void rotateRecur(int[][] matrix, int curX, int curY, int len){ 9 if (len==1 || len==0) return;10 11 for (int i=0;i<len-1;i++){12 int temp = matrix[curX][curY+i];13 matrix[curX][curY+i] = matrix[curX+len-1-i][curY];14 matrix[curX+len-1-i][curY] = matrix[curX+len-1][curY+len-1-i];15 matrix[curX+len-1][curY+len-1-i] = matrix[curX+i][curY+len-1];16 matrix[curX+i][curY+len-1] = temp;17 }18 rotateRecur(matrix,curX+1,curY+1,len-2);19 }20 21 }
Solution2:
We can easily write the method into iterative method.
1 public class Solution { 2 public void rotate(int[][] matrix) { 3 int mLen = matrix.length; 4 5 for (int j=0;j<mLen/2;j++){ 6 int curX = j; 7 int curY = j; 8 int len = mLen-j*2; 9 10 for (int i=0;i<len-1;i++){11 int temp = matrix[curX][curY+i];12 matrix[curX][curY+i] = matrix[curX+len-1-i][curY];13 matrix[curX+len-1-i][curY] = matrix[curX+len-1][curY+len-1-i];14 matrix[curX+len-1][curY+len-1-i] = matrix[curX+i][curY+len-1];15 matrix[curX+i][curY+len-1] = temp;16 }17 18 }19 20 } 21 }
Leetcode-Rotate Image
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