Add D implementation of monte carlo (#162)

* Add d implementation of monte carlo

* cleanup d version of monte carlo

Author: SirSireesh

chapters/monte_carlo/code/d/monte_carlo.d

@@ -0,0 +1,29 @@
+///Returns true if a point (x, y) is in the circle with radius r
+bool inCircle(real x, real y)
+{
+    return x ^^ 2 + y ^^ 2 < 1.0;
+}
+
+///Calculate pi using monte carlo
+real monteCarloPI(ulong n)
+{
+    import std.algorithm : count;
+    import std.random : uniform01;
+    import std.range : generate, take;
+    import std.typecons : tuple;
+
+    auto piCount =  generate(() => tuple!("x", "y")(uniform01, uniform01))
+        .take(n)
+        .count!(a => inCircle(a.x, a.y));
+    return piCount * 4.0 / n;
+}
+
+void main()
+{
+    import std.math : abs, PI;
+    import std.stdio : writeln;
+
+    auto p = monteCarloPI(100_000);
+    writeln("Estimated pi: ", p);
+    writeln("Percent error: ", abs(p - PI) * 100 / PI);
+}

chapters/monte_carlo/monte_carlo.md

@@ -45,6 +45,8 @@ each point is tested to see whether it's in the circle or not:
 [import:7-7, lang:"haskell"](code/haskell/monteCarlo.hs)
 {% sample lang="rs" %}
 [import:7-9, lang:"rust"](code/rust/monte_carlo.rs)
+{% sample lang="d" %}
+[import:2-5, lang:"d"](code/rust/monte_carlo.d)
 {% endmethod %}
 
 If it's in the circle, we increase an internal count by one, and in the end,
@@ -88,6 +90,9 @@ Feel free to submit your version via pull request, and thanks for reading!
 {%sample lang="rs" %}
 ### Rust
 [import, lang:"rust"](code/rust/monte_carlo.rs)
+### D
+{%sample lang="d" %}
+[import, lang:"d"](code/d/monte_carlo.d)
 {% endmethod %}