aoc71.py

fname = "7_input.txt"
import numpy as np

with open(fname) as f:
    xi = np.array([int(c) for c in f.readline().strip().split(",")], dtype=int)

def costfun(x, xi):
    return sum([sum(range(abs(x-xii)+1)) for xii in xi])

def direction(x, xi):
    plus = costfun(x+1, xi)
    minus = costfun(x-1, xi)
    if plus > minus:
        return -1
    else:
        return 1

N = len(xi)
# init guess
x = round(sum(xi)/N)

done = False
cost0 = costfun(x,xi)
i = 1
while not done:
    x += direction(x, xi)
    cost = costfun(x,xi)
    print(f"Iteration {i}, Cost: {cost}")
    if cost > cost0:
        done = True
    cost0 = cost
    i+=1