Skip to content

Instantly share code, notes, and snippets.

@algomaster99
Created April 24, 2020 11:34
Show Gist options
  • Save algomaster99/782b898177ca37bfbf955cec416bb6a4 to your computer and use it in GitHub Desktop.
Save algomaster99/782b898177ca37bfbf955cec416bb6a4 to your computer and use it in GitHub Desktop.
Solution to Doomsday Fuel foobar challenge
from fractions import Fraction
# Replace trials by probabilties of occurrences
def replace_probability(m):
for row in range(len(m)):
total = 0
for item in range(len(m[row])):
total += m[row][item]
if total != 0:
for item in range(len(m[row])):
m[row][item] /= float(total)
return m
# R - non-terminal -> terminal
# Q - non-terminal -> non-terminal
def RQ(m, terminal_state, non_terminal_state):
R = []
Q = []
for i in non_terminal_state:
temp_t = []
temp_n = []
for j in terminal_state:
temp_t.append(m[i][j])
for j in non_terminal_state:
temp_n.append(m[i][j])
R.append(temp_t)
Q.append(temp_n)
return R, Q
# Get Identity Matrix - Q
def subtract_Q_from_identity(Q):
"""
If Q = [
[1,2,3],
[4,5,6],
[7,8,9],
]
I - Q:
[[1,0,0] [[0,-2,-3]
[0,1,0] - Q = [-4,-4,-6]
[0,0,1]] [-7,-8,-8]]
"""
n = len(Q)
for row in range(len(Q)):
for item in range(len(Q[row])):
if row == item:
Q[row][item] = 1 - Q[row][item]
else:
Q[row][item] = -Q[row][item]
return Q
# Get minor matrix
def get_minor_matrix(Q,i,j):
"""
Q = [
[1,2,3],
[4,5,6],
[7,8,9],
]
Minor matrix corresponding to 0,0 is
[
[5,6],
[8,9],
]
"""
minor_matrix = []
for row in Q[:i] + Q[i+1:]:
temp = []
for item in row[:j] + row[j+1:]:
temp.append(item)
minor_matrix.append(temp)
return minor_matrix
# Get determinant of a square matrix
def get_determinant(Q):
if len(Q) == 1:
return Q[0][0]
if len(Q) == 2:
return Q[0][0]*Q[1][1] - Q[0][1]*Q[1][0]
determinant = 0
for first_row_item in range(len(Q[0])):
minor_matrix = get_minor_matrix(Q, 0, first_row_item)
determinant += (((-1)**first_row_item)*Q[0][first_row_item] * get_determinant(minor_matrix))
return determinant
# Get transpose of a square matrix
def get_transpose_square_matrix(Q):
for i in range(len(Q)):
for j in range(i, len(Q), 1):
Q[i][j], Q[j][i] = Q[j][i], Q[i][j]
return Q
def get_inverse(Q):
Q1 = []
for row in range(len(Q)):
temp = []
for column in range(len(Q[row])):
minor_matrix = get_minor_matrix(Q, row, column)
determinant = get_determinant(minor_matrix)
temp.append(((-1)**(row+column))*determinant)
Q1.append(temp)
main_determinant = get_determinant(Q)
Q1 = get_transpose_square_matrix(Q1)
for i in range(len(Q)):
for j in range(len(Q[i])):
Q1[i][j] /= float(main_determinant)
return Q1
def multiply_matrix(A, B):
result = []
dimension = len(A)
for row in range(len(A)):
temp = []
for column in range(len(B[0])):
product = 0
for selector in range(dimension):
product += (A[row][selector]*B[selector][column])
temp.append(product)
result.append(temp)
return result
def gcd(a ,b):
if b==0:
return a
else:
return gcd(b,a%b)
def sanitize(M):
needed = M[0]
to_fraction = [Fraction(i).limit_denominator() for i in needed]
lcm = 1
for i in to_fraction:
if i.denominator != 1:
lcm = i.denominator
for i in to_fraction:
if i.denominator != 1:
lcm = lcm*i.denominator/gcd(lcm, i.denominator)
to_fraction = [(i*lcm).numerator for i in to_fraction]
to_fraction.append(lcm)
return to_fraction
def solution(m):
n = len(m)
if n==1:
if len(m[0]) == 1 and m[0][0] == 0:
return [1, 1]
terminal_state = []
non_terminal_state = []
# Get terminal and non-terminal states
for row in range(len(m)):
count = 0
for item in range(len(m[row])):
if m[row][item] == 0:
count += 1
if count == n:
terminal_state.append(row)
else:
non_terminal_state.append(row)
# Replace trials by probabilties
probabilities = replace_probability(m)
# Get R and Q matrix
R, Q = RQ(probabilities, terminal_state, non_terminal_state)
IQ = subtract_Q_from_identity(Q)
# Get Fundamental Matrix (F)
IQ1 = get_inverse(IQ)
product_IQ1_R = multiply_matrix(IQ1, R)
return sanitize(product_IQ1_R)
# Case where state 0 itself is a terminal state
assert(solution(
[
[0],
]
)) == [1, 1]
assert(solution(
[
[0, 2, 1, 0, 0],
[0, 0, 0, 3, 4],
[0, 0, 0, 0, 0],
[0, 0, 0, 0, 0],
[0, 0, 0, 0, 0],
]
)) == [7, 6, 8, 21]
assert(solution(
[
[0, 1, 0, 0, 0, 1],
[4, 0, 0, 3, 2, 0],
[0, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0],
]
)) == [0, 3, 2, 9, 14]
@z-ding
Copy link

z-ding commented May 15, 2023

Does anybody know why my code works fine for the two given test cases in my IDE, but it fails all test cases in foobar?
import numpy as np
from fractions import Fraction
#from fractions import gcd #python 2.7
from math import gcd
def solution(m):
#ai represents the chance of starting from state i and going to certain terminal state
'''
[
[0,1,0,0,0,1], # s0, the initial state, goes to s1 and s5 with equal probability
[4,0,0,3,2,0], # s1 can become s0, s3, or s4, but with different probabilities
[0,0,0,0,0,0], # s2 is terminal, and unreachable (never observed in practice)
[0,0,0,0,0,0], # s3 is terminal
[0,0,0,0,0,0], # s4 is terminal
[0,0,0,0,0,0], # s5 is terminal
]
Terminal state 5:
a0 = 0.5 + 0.5a1
a1 = 4/9a0
=> a0 = 9/14, a1 = 2/7
terminal 5 = 9/14
Terminal state 3:
a0 = 0.5a1
a1 = 4/9a0 + 3/9
a0 = 3/14, a1 = 3/7
terminal 3 = 3/14
Terminal state 4:
a0 = 0.5a1
a1 = 4/9a0 + 2/9
a0 = 1/7, a1 = 2/7
Terminal 4: 1/7
ans = 0:3/14:1/7:9/14 = 0:3:2:9
'''
#find all terminal state
def lcm(x, y):
return x * y // gcd(x, y)
Terminal = set()
ans = []
res = []
l = 1 # lcm of demoninator
for i in range(1,len(m)):
isTerminal = True
for j in range(0, len(m[i])):
if m[i][j] !=0:
isTerminal = False
break
if isTerminal == True:
Terminal.add(i)
#convert each line into probability
terminal =[]
for elem in Terminal:
terminal.append(elem)
terminal.sort()
for i in range(0,len(m)):
ttl = 0
if i not in terminal:
for j in range(0, len(m[i])):
ttl += m[i][j]
for j in range(0, len(m[i])):
m[i][j] =m[i][j]/ttl
#loop for each terminal state, list out the linear equation and solve it
lc = 1#lcm
for t in terminal:
#define coefficient matrix and constant vector
vector = []
coei = []
for i in range(0,len(m)):
if i in terminal:#terminal state
continue
con = 0
c = [1] *(len(m)-len(terminal))# current state's coefficient is 1
for j in range(0, len(m[i])):
if j ==i:
continue
if j in terminal:
if j==t:
con = m[i][j]
else:#not terminal state
c[j]=-m[i][j]
vector.append(con)
coei.append(list(c))
y = np.linalg.solve(coei, vector)
# Convert the solution to fractions
y_fraction = [Fraction(num).limit_denominator() for num in y]
numerator = y_fraction[0].numerator
denominator = y_fraction[0].denominator
lc = lcm(lc,denominator)
res.append([numerator,denominator])
for r in res:
a = int(r[0]*lc//r[1])
ans.append(a)
ans.append(int(lc))
return ans

@JingxuOuyang
Copy link

天才,我大概看懂了题解,实在是不知道怎么用保持分数的形式进行运算,比如说求逆

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment