vault backup: 2022-09-02 16:12:45

OJ notes/pages/Leetcode Rotate-Image.md

@@ -54,7 +54,43 @@ Mainly two ways
 
 #### Method 1: rotate in rings
 
+#TODO complete in this method.
+
 #### Method 2: transpose and reflect
 
+transpose reflects the matrix in `y = x`,
+reflect changes matrix in axis y
+
 ### Solution
 
+```cpp
+class Solution {
+
+  void reflect(vector<vector<int>> &mat) {
+    // reflect in y axis.
+    int n = mat.size();
+    for (int i = 0; i < n; i++) {
+      for (int j = 0, half = n / 2; j < half; j++) {
+        swap(mat[i][j], mat[i][n - j - 1]);
+      }
+    }
+  }
+
+  void transpose(vector<vector<int>> &mat) {
+    int n = mat.size();
+    for (int i = 0; i < n; i++) {
+      for (int j = 0; j < i; j++) {
+        swap(mat[i][j], mat[j][i]);
+      }
+    }
+  }
+
+public:
+  void rotate(vector<vector<int>> &matrix) {
+    // transpose and reflect
+
+    transpose(matrix);
+    reflect(matrix);
+  }
+};
+```