Initial data commit

Task/Pells-equation/D/pells-equation.d

@@ -0,0 +1,41 @@
+import std.bigint;
+import std.math;
+import std.stdio;
+
+void fun(ref BigInt a, ref BigInt b, int c) {
+    auto t = a;
+    a = b;
+    b = b * c + t;
+}
+
+void solvePell(int n, ref BigInt a, ref BigInt b) {
+    int x = cast(int) sqrt(cast(real) n);
+    int y = x;
+    int z = 1;
+    int r = x << 1;
+    BigInt e1 = 1;
+    BigInt e2 = 0;
+    BigInt f1 = 0;
+    BigInt f2 = 1;
+    while (true) {
+        y = r * z - y;
+        z = (n - y * y) / z;
+        r = (x + y) / z;
+        fun(e1, e2, r);
+        fun(f1, f2, r);
+        a = f2;
+        b = e2;
+        fun(b, a, x);
+        if (a * a - n * b * b == 1) {
+            return;
+        }
+    }
+}
+
+void main() {
+    BigInt x, y;
+    foreach(n; [61, 109, 181, 277]) {
+        solvePell(n, x, y);
+        writefln("x^2 - %3d * y^2 = 1 for x = %27d and y = %25d", n, x, y);
+    }
+}