image rotation problem

rotateimage.cpp

@@ -0,0 +1,35 @@
+/*
+You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).
+
+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.
+
+ */
+/*
+ * clockwise rotate
+ * first reverse up to down, then swap the symmetry 
+ * 1 2 3     7 8 9     7 4 1
+ * 4 5 6  => 4 5 6  => 8 5 2
+ * 7 8 9     1 2 3     9 6 3
+*/
+void rotate(vector<vector<int> > &matrix) {
+    reverse(matrix.begin(), matrix.end());
+    for (int i = 0; i < matrix.size(); ++i) {
+        for (int j = i + 1; j < matrix[i].size(); ++j)
+            swap(matrix[i][j], matrix[j][i]);
+    }
+}
+
+/*
+ * anticlockwise rotate
+ * first reverse left to right, then swap the symmetry
+ * 1 2 3     3 2 1     3 6 9
+ * 4 5 6  => 6 5 4  => 2 5 8
+ * 7 8 9     9 8 7     1 4 7
+*/
+void anti_rotate(vector<vector<int> > &matrix) {
+    for (auto vi : matrix) reverse(vi.begin(), vi.end());
+    for (int i = 0; i < matrix.size(); ++i) {
+        for (int j = i + 1; j < matrix[i].size(); ++j)
+            swap(matrix[i][j], matrix[j][i]);
+    }
+}