From 743966c7b803612cf17df95c19c039ba4d229e4e Mon Sep 17 00:00:00 2001
From: felixm <mail@felixm.de>
Date: Thu, 28 Sep 2023 23:23:55 +0200
Subject: [PATCH] Solve e816 because I have to get easy ones for my Euler goal.

---
 python/e816.py                 | 39 ++++++++++++++++++++++++++++++++++
 python/lib_create_templates.py | 17 +++++++++------
 2 files changed, 49 insertions(+), 7 deletions(-)
 create mode 100644 python/e816.py

diff --git a/python/e816.py b/python/e816.py
new file mode 100644
index 0000000..60e0d4a
--- /dev/null
+++ b/python/e816.py
@@ -0,0 +1,39 @@
+from math import sqrt
+
+
+def distance(p1, p2) -> float:
+    return (p1[0] - p2[0]) ** 2 + (p1[1] - p2[1]) ** 2
+
+
+def points(k: int):
+    s = 290797
+    mod = 50515093
+    # s = 5
+    # mod = 23
+    points = []
+    for _ in range(k):
+        sn = (s ** 2) % mod
+        p = (s, sn)
+        points.append(p)
+        s = (sn ** 2) % mod
+    return points
+
+
+def euler_816():
+    ps = sorted(points(2000000), key=lambda p: p[0])
+    d_min = float("inf")
+    sweep_dist = 5  # heuristic
+    for i in range(len(ps)):
+        for j in range(i, min(i + sweep_dist, len(ps))):
+            if i == j:
+                continue
+            d  = distance(ps[i], ps[j])
+            if d < d_min:
+                d_min = d
+    return round(sqrt(d_min), 9)
+
+
+if __name__ == "__main__":
+    solution = euler_816()
+    print("e816.py: " + str(solution))
+    assert(solution == 20.880613018)
diff --git a/python/lib_create_templates.py b/python/lib_create_templates.py
index 54ad75e..7a4b82e 100644
--- a/python/lib_create_templates.py
+++ b/python/lib_create_templates.py
@@ -1,5 +1,4 @@
-FROM = 100
-TILL = 100
+import sys
 
 TEMPLATE = """
 def euler_XXX():
@@ -14,13 +13,17 @@ if __name__ == "__main__":
 """
 
 
-for i in range(FROM, TILL + 1):
-    if i < 100:
-        e = "0" + str(i)
-    else:
-        e = str(i)
+def main():
+    try:
+        e = sys.argv[1]
+    except IndexError:
+        print("Provide Euler problem number for which to create template.")
+        return
     filename = "e" + e + ".py"
     with open(filename, "w") as f:
         s = TEMPLATE.replace("XXX", e)
         f.write(s)
 
+
+if __name__ == "__main__":
+    main()