From efa0de090f4114ffb234e15f554e976810f7cd07 Mon Sep 17 00:00:00 2001
From: Ivan Malison <IvanMalison@gmail.com>
Date: Tue, 17 Nov 2015 06:03:44 -0800
Subject: [PATCH] plus minus

---
 dotfiles/lib/python/plus_minus.py | 63 +++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 dotfiles/lib/python/plus_minus.py

diff --git a/dotfiles/lib/python/plus_minus.py b/dotfiles/lib/python/plus_minus.py
new file mode 100644
index 00000000..ecccdd09
--- /dev/null
+++ b/dotfiles/lib/python/plus_minus.py
@@ -0,0 +1,63 @@
+def groupings(numbers):
+    if len(numbers) == 0:
+        raise StopIteration()
+    if len(numbers) == 1:
+        yield ((numbers[0],),)
+        raise StopIteration()
+    this_number = numbers[0]
+    this_tuple = (this_number,)
+    next_groupings = groupings(numbers[1:])
+    for grouping in next_groupings:
+        yield (this_tuple,) + grouping
+        yield (this_tuple + grouping[0],) + grouping[1:]
+
+
+def plus_minus_n(numbers, n):
+    for grouping in groupings(numbers):
+        numbers = map(group_to_int, grouping)
+        pms = plus_minuses(len(numbers) - 1)
+        for pm in pms:
+            result = compute(numbers, pm)
+            string = generate_string(numbers, pm)
+            if result == n:
+                yield string
+
+
+def generate_string(numbers, pms):
+    string = ''
+    for number in numbers:
+        string += '{0}'.format(number)
+        if pms:
+            string += '+' if pms[0] is PLUS else '-'
+            pms = pms[1:]
+    return string
+
+
+def compute(numbers, plus_minus):
+    sum = numbers[0]
+    remaining = numbers[1:]
+    while remaining:
+        if plus_minus[0] == PLUS:
+            sum += remaining[0]
+        else:
+            sum -= remaining[0]
+        remaining = remaining[1:]
+        plus_minus = plus_minus[1:]
+    return sum
+
+
+def group_to_int(group):
+    return int(''.join(map(str, group)))
+
+
+PLUS = object()
+MINUS = object()
+
+
+def plus_minuses(n):
+    if n == 0:
+        yield ()
+        raise StopIteration()
+    for pm in plus_minuses(n-1):
+        yield (PLUS,) + pm
+        yield (MINUS,) + pm