leetcode 048 Rotate Image

walter1990

于 2016-04-29 22:14:55 发布

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本文介绍了一个用于二维矩阵(图像)的90度顺时针旋转算法，并实现了原地(in-place)旋转的功能。通过循环交换矩阵元素的方式，有效地完成了旋转操作。

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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?

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class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int rows = matrix.size(), cols = matrix[0].size();
 
		int uprow = 0, downrow = rows-1, leftcol = 0, rightcol = cols-1;

		for(; uprow < downrow; uprow++, downrow--) {
			int ax = uprow, ay = leftcol;
			int bx = uprow, by = rightcol;
			int cx = downrow, cy = leftcol;
			int dx = downrow, dy = rightcol;

            int cnt = downrow-uprow;
            
			while(cnt--) {
                
				int temp = matrix[bx][by];
				matrix[bx][by] = matrix[ax][ay];
				matrix[ax][ay] = matrix[cx][cy];
				matrix[cx][cy] = matrix[dx][dy];
				matrix[dx][dy] = temp;
                
				ay+=1;
				bx+= 1;
				cx-=1;
				dy-=1;
			}

			leftcol++;
			rightcol--;
			
			
		}
    }
};