# How Voting Systems Work 8, Exercise 1: efficiency gap of a six-district map
# Assumed, invented tallies (votes for party A, votes for party B) in six districts.
districts = [(5200, 4800), (4100, 5900), (3300, 6700), (6100, 3900), (4600, 5400), (4400, 5600)]

def wasted(a, b):
    needed = (a + b) // 2 + 1
    return (a - needed, b) if a > b else (a, b - needed)

wa = wb = total = 0
for i, (a, b) in enumerate(districts, 1):
    x, y = wasted(a, b)
    wa, wb, total = wa + x, wb + y, total + a + b
    print(f"district {i}: A {a:>5}  B {b:>5}  wasted A {x:>5}  wasted B {y:>5}")
gap = (wa - wb) / total
print(f"total wasted: A {wa}, B {wb}; total votes {total}")
print(f"A vote share {sum(a for a, b in districts) / total:.1%}, A seats {sum(a > b for a, b in districts)}/{len(districts)}")
print(f"efficiency gap {gap:+.1%} ->", "favours B" if gap > 0 else "favours A")
print("above an 8% flag" if abs(gap) >= 0.08 else "below an 8% flag")

# Output when run:
# district 1: A  5200  B  4800  wasted A   199  wasted B  4800
# district 2: A  4100  B  5900  wasted A  4100  wasted B   899
# district 3: A  3300  B  6700  wasted A  3300  wasted B  1699
# district 4: A  6100  B  3900  wasted A  1099  wasted B  3900
# district 5: A  4600  B  5400  wasted A  4600  wasted B   399
# district 6: A  4400  B  5600  wasted A  4400  wasted B   599
# total wasted: A 17698, B 12296; total votes 60000
# A vote share 46.2%, A seats 2/6
# efficiency gap +9.0% -> favours B
# above an 8% flag