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diff --git a/lab01/Triplet.hh b/lab01/Triplet.hh
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+/*
+ * Triplet.hh
+ *
+ * Template implementation of the Triplet abstract data type.
+ * The class also provides basic three-dimensional vector operations.
+ */
+
+#include <array>
+#include <cstddef>
+#include <algorithm>
+
+/**
+ * A generic three-element tuple.
+ *
+ * In this experiment, Triplet is also treated as a three-dimensional
+ * vector, supporting vector addition, subtraction, scalar multiplication
+ * and dot product.
+ *
+ * T is the element type of the triplet.
+ */
+template<typename T>
+class Triplet {
+public:
+  Triplet (T a, T b, T c) : data_{a, b, c} {}
+
+  T &operator[] (std::size_t i) {
+    return data_[i];
+  }
+
+  const T &operator[] (std::size_t i) const
+  {
+    return data_[i];
+  }
+
+  Triplet operator+ (const Triplet &rhs) const
+  {
+    return Triplet (data_[0] + rhs.data_[0],
+                    data_[1] + rhs.data_[1],
+                    data_[2] + rhs.data_[2]);
+  }
+
+  Triplet operator- (const Triplet &rhs) const
+  {
+    return Triplet (data_[0] - rhs.data_[0],
+                    data_[1] - rhs.data_[1],
+                    data_[2] - rhs.data_[2]);
+  }
+
+  /* Scalar multiplication: vector * scalar.  */
+  Triplet operator* (const T& scalar)  const
+  {
+    return Triplet(
+                   data_[0] * scalar,
+                   data_[1] * scalar,
+                   data_[2] * scalar);
+  }
+
+  /* Scalar multiplication: scalar * vector.  */
+  friend Triplet
+  operator* (const T &scalar, const Triplet &v) {
+    return v * scalar;
+  }
+
+  /* Dot product of two three-dimensional vectors.  */
+  T operator* (const Triplet &rhs) const {
+    return data_[0] * rhs.data_[0]
+       + data_[1] * rhs.data_[1]
+       + data_[2] * rhs.data_[2];
+  }
+
+  T max () const {
+    return *std::max_element (data_.begin (), data_.end ());
+  }
+
+  T min() const {
+    return *std::min_element( data_.begin (), data_.end ());
+  }
+
+  /* Return true if the elements are in nondecreasing order.  */
+  bool is_ascending() const {
+    return data_[0] <= data_[1] && data_[1] <= data_[2];
+  }
+
+  /* Return true if the elements are in nonincreasing order.  */
+  bool is_descending() const {
+    return data_[0] >= data_[1] && data_[1] >= data_[2];
+  }
+  
+private:
+  std::array<T, 3> data_;  
+};