Add chrono

Author: mortennobel

README.md

@@ -447,7 +447,7 @@ a.first; // "hello"
 a.second; // 3
 ```
 
-## `map` (associative array - usually implemented as binary search trees)
+## `map` (associative array - usually implemented as binary search trees - avg. time complexity: O(log n))
 
 ```cpp
 #include <map> // Include map (std namespace)
@@ -458,7 +458,7 @@ for (auto& p:a)
 a.size(); // 1
 ```
 
-## `unordered_map` (associative array - usually implemented as hash table)
+## `unordered_map` (associative array - usually implemented as hash table - avg. time complexity: O(1))
 
 ```cpp
 #include <unordered_map> // Include map (std namespace)
@@ -469,7 +469,7 @@ for (auto& p:a)
 a.size(); // 1
 ```
 
-## `set` (store unique elements - usually implemented as binary search trees)
+## `set` (store unique elements - usually implemented as binary search trees - avg. time complexity: O(log n))
 
 ```cpp
 #include <set> // Include set (std namespace)
@@ -480,7 +480,7 @@ if (s.find(123) != s.end()) // Search for an element
 cout << s.size(); // Number of elements in set
 ```
 
-## `unordered_set` (store unique elements - usually implemented as a hash set)
+## `unordered_set` (store unique elements - usually implemented as a hash set - avg. time complexity: O(1))
 
 ```cpp
 #include <unordered_set> // Include set (std namespace)
@@ -501,3 +501,18 @@ sort(a, a+n); // Sort array a[0]..a[n-1] by <
 sort(a.begin(), a.end()); // Sort vector or deque
 reverse(a.begin(), a.end()); // Reverse vector or deque
 ```
+
+## 'chrono' (Time related library)
+```cpp
+#include <chrono> // Include chrono
+using namespace chrono; // Use namespace
+auto from = // Get current time_point
+ high_resolution_clock::now();
+// ... do some work 
+auto to = // Get current time_point
+ high_resolution_clock::now();
+using ms = // Compute duration in milliseconds
+ duration<float, milliseconds::period>;
+cout << duration_cast<ms>(to - from)
+ .count() << "ms";
+```