原地旋转矩阵(不申请新的内存空间旋转矩阵)
Given an image represented by an NxN matrix, where each pixel in the imageis 4bytes, write a method to rotate the image by 90 degrees Can you do this in place?
描述:给定一个N*N的图像,每个位置的像素是4byte,写一个方法用来在原来的空间内旋转图像90度。
思路:我们可以按层来旋转。
void matrixRotation(int [][]a,int n) { for(int layer=0;layer<n;layer++) { int first=layer; int last = n-layer-1; for(int i=first;i<last;i++) { int offset=i-first; int top =a[first][i]; a[first][i]=a[last-offset][first];//left->top a[last-offset][first]=a[last][last-offset];//bottom->left a[last][last-offset]=a[i][last];//right->bottom a[i][last]=top;//top->right } } }