September Morn Update

Task/Equilibrium-index/Python/equilibrium-index-6.py

@@ -0,0 +1,56 @@
+"""Equilibrium index"""
+
+from itertools import (accumulate)
+
+
+# equilibriumIndices :: [Num] -> [Int]
+def equilibriumIndices(xs):
+    '''List indices at which the sum of values to the left
+       equals the sum of values to the right.'''
+    def go(xs):
+        '''Left scan from accumulate, right scan derived from left'''
+        ls = list(accumulate(xs))
+        n = ls[-1]
+        return [i for (i, (x, y)) in enumerate(zip(
+            ls,
+            [n] + [n - x for x in ls[0:-1]]
+        )) if x == y]
+    return go(xs) if xs else []
+
+
+# TEST -------------------------------------------------
+# main :: IO ()
+def main():
+    '''Tabulated test results'''
+    print(
+        tabulated('Equilibrium indices:\n')(
+            equilibriumIndices
+        )([
+            [-7, 1, 5, 2, -4, 3, 0],
+            [2, 4, 6],
+            [2, 9, 2],
+            [1, -1, 1, -1, 1, -1, 1],
+            [1],
+            []
+        ])
+    )
+
+
+# GENERIC -------------------------------------------------
+
+
+# tabulated :: String -> (a -> b) -> [a] -> String
+def tabulated(s):
+    '''heading -> function -> input List -> tabulated output string'''
+    def go(f, xs):
+        def width(x):
+            return len(str(x))
+        w = width(max(xs, key=width))
+        return s + '\n' + '\n'.join([
+            str(x).rjust(w, ' ') + ' -> ' + str(f(x)) for x in xs
+        ])
+    return lambda f: lambda xs: go(f, xs)
+
+
+if __name__ == '__main__':
+    main()