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追記

2017/10/19 00:54

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スコア16614

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@@ -1 +1,105 @@
 `std::valarray<double>` を sliceする方が万倍楽ちゃいますか?
+[追記]
+columnを返すのやってみた:
+```C++
+#include <iostream>
+#include <algorithm>
+template<typename T>
+class column {
+public:
+  column(T* data, size_t cols) : data_(data), cols_(cols) {}
+  T& operator[](size_t row) { return data_[cols_*row]; }
+private:
+  T* data_;
+  size_t cols_;
+};
+template<typename T>
+class matrix {
+public:
+  matrix(size_t rows, size_t cols) : cols_(cols), rows_(rows) {
+    data_ = new T[rows*cols];
+  }
+  ~matrix() { delete[] data_; }
+  void fill(const T& val) { std::fill_n(data_, rows_*cols_, val); }
+  column<T> operator()(size_t col) { return column<T>(data_+col, cols_); }
+  T* operator[](size_t row) { return data_+cols_*row; }
+private:
+  T* data_;
+  size_t cols_;
+  size_t rows_;
+};
+// おためし
+int main() {
+  using namespace std;
+  matrix<double> mtx(2,3);
+  mtx.fill(0.0);
+  column<double> clm = mtx(1);
+  clm[0] = 1.23;
+  clm[1] = 2.34;
+  for ( size_t r = 0; r < 2; ++r ) {
+    for ( size_t c = 0; c < 3; ++c ) {
+      cout << mtx[r][c] << ' ';
+    }
+    cout << endl;
+  }
+}
+```