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Why Python recursive function returns None [duplicate]
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Recursive function does not return specified value
(2 answers)
Closed 1 year ago.
I have written a maze solver program. I want the PathFinder function to return True if a path is found and then print the path or else simply return False. But my program always keeps returning False even if a path is found. It would be great if you guys can help me figure this out.
def findPaths(m,path,i,j):
r,c = len(m), len(m[0])
if i == r-1 and j == c-1:
print(path)
return True
#explore
path.append(m[i][j])
# move down
if i != r-1 and m[i+1][j] == '↓ ':
findPaths(m,path,i+2,j)
#move up
if i < 0 and m[i-1][j] == '↑ ':
findPaths(m,path,i-2,j)
#move right
if j != c-1 and m[i][j+1] == '→':
findPaths(m,path,i,j+2)
#move left
if j > 0 and m[i][j-1] == '←':
findPaths(m,path,i,j-2)
path.pop()
def maze(r,c):
m = []
for i in range(r):
row = []
for j in range(1, c + (c)):
rand_num = str(randint(1, 99))
if j % 2 != 0:
if len(rand_num) == 1:
row.append(' ' + rand_num)
else:
row.append(rand_num)
else:
row.append('?')
m.append(row)
up_left_count = r * c // 3
down_right_count = r * c * 2 // 3
for v in range(r + (r - 1)):
vertical_lst = []
for each in range(1, c + c):
if each % 2 == 0:
vertical_lst.append(' ')
else:
vertical_lst.append('? ')
if v % 2 != 0:
m.insert(v, vertical_lst)
idx_i = []
idx_j = []
idx_v_i = []
idx_v_j = []
for i in range(len(m)):
for j in range(len(m[0])):
if i % 2 == 0 and j % 2 != 0:
idx_i.append(i)
idx_j.append(j)
for v_i in range(len(m)):
for v_j in range(len(m[0])):
if v_i % 2 != 0 and v_j % 2 == 0:
idx_v_i.append(v_i)
idx_v_j.append(v_j)
idx_i = list(set(idx_i))
idx_j = list(set(idx_j))
idx_v_i = list(set(idx_v_i))
idx_v_j = list(set(idx_v_j))
for count in range(up_left_count):
i_int = randint(0, len(idx_i) - 1)
j_int = randint(0, len(idx_j) - 1)
if m[i_int][j_int] != '←':
m[idx_i[i_int]][idx_j[j_int]] = '←'
for count_v in range(up_left_count):
i_v_int = randint(0, len(idx_v_i) - 1)
j_v_int = randint(0, len(idx_v_j) - 1)
if m[i_v_int][j_v_int] != '↑':
m[idx_v_i[i_v_int]][idx_v_j[j_v_int]] = '↑ '
for i in range(len(m)):
for j in range(len(m[0])):
if i % 2 == 0 and j % 2 != 0:
if m[i][j] == '?':
m[i][j] = '→'
for i in range(len(m)):
for j in range(len(m[0])):
if i % 2 != 0 and j % 2 == 0:
if m[i][j] != '↑ ':
m[i][j] = '↓ '
m[0][0] = "S"
m[-1][-1] = "D"
for i in range(len(m)):
for j in range(len(m[0])):
print(m[i][j], end=" ")
print()
path = []
return findPaths(m, path, 0,0)
if maze(5,6):
print('True')
else:
print('False')
I want to inset new key,value pair into a variable that was not previously defined
Here is what i want to do:
def drawboard(nextmove):
result = nextmove
pos = 1
print result
for i in range(7):
for j in range(7):
if (j == 0 or i % 2 == 0 or j % 2 == 0):
print '*',
if (i % 2 != 0 and j % 2 != 0):
print pos,
pos += 1
if (j == 6):
print '\n'
move = raw_input("Input you move(i.e. x,3[position, your symbol]: ")
if move == 'q':
exit()
calcres(move)
def calcres(move):
nextmove = dict([move.split(',')])
drawboard(nextmove)
drawboard({0: 0})
Inside drawboard function i want to concatenate nextmove with result, and save all the moves inside the result finally. I tried initializing result = {} but as expected that removes all items from result and re-initializes it resulting only one item inside that dictionary.
Use setdefault to initialize the result dictionary value to an empty list whenever the key is not present
def drawboard(nextmove):
result.setdefault(nextmove[0],[]).append(nextmove[1])
pos = 1
#print result
for i in range(7):
for j in range(7):
if (j == 0 or i % 2 == 0 or j % 2 == 0):
print '*',
if (i % 2 != 0 and j % 2 != 0):
print pos,
pos += 1
if (j == 6):
print '\n'
move = raw_input("Input you move(i.e. x,3[position, your symbol]: ")
if move == 'q':
exit()
calcres(move)
def calcres(move):
nextmove = move.split(',')
drawboard(nextmove)
result = {}
drawboard([0,0])
I am fairly new to python, I am not sure on how to fix a index string out of range. it happens right after the while loop when I want to send mylist[i][0] to formatting function. Any pointer on my code in general would be awesome!
def formatting(str1):
if str1 == '?':
return True
else:
return False
while(i <= len(mylist)):
val = formatting(mylist[i][0])
if val == True:
str1 = mylist[i]
str2 = mylist[i+1]
i = i + 2
format_set(str1, str2)
else:
if format == True:
if (margin + count + len(mylist[i])) <= width:
if (i == (len(mylist)-1)):
list2.append(mylist[i])
print(" " * margin + " ".join(list2))
break
list2.append(mylist[i])
count += len(mylist[i])
i += 1
else:
print(" " * margin + " ".join(list2))
list2 = []
count = 0
else:
temp_margin = margin
temp_width = width
width = 60
margin = 0
if (margin + count + len(mylist[i])) <= width:
if (i == (len(mylist)-1)):
list2.append(mylist[i])
print(" " * margin + " ".join(list2))
margin = temp_margin
width = temp_width
break
list2.append(mylist[i])
count += len(mylist[i])
i += 1
else:
print(" " * margin + " ".join(list2))
list2 = []
count = 0
change
i <= len(mylist)
to
i < len(mylist)
In the last iteration of the while loop, i is referring to the last value. Hence,
str2 = mylist[i+1]
is trying to reference a string outside the allowed range and you get an error.
EDIT: Also, as Wcrousse mentioned, the while (i <= len(...)) should be changed to i < len(...) because indexes go from 0 - (length-1).
If I have 2 numbers in binary form as a string, and I want to add them I will do it digit by digit, from the right most end. So 001 + 010 = 011
But suppose I have to do 001+001, how should I create a code to figure out how to take carry over responses?
bin and int are very useful here:
a = '001'
b = '011'
c = bin(int(a,2) + int(b,2))
# 0b100
int allows you to specify what base the first argument is in when converting from a string (in this case two), and bin converts a number back to a binary string.
This accepts an arbitrary number or arguments:
>>> def bin_add(*bin_nums: str) -> str:
... return bin(sum(int(x, 2) for x in bin_nums))[2:]
...
>>> x = bin_add('1', '10', '100')
>>> x
'111'
>>> int(x, base = 2)
7
Here's an easy to understand version
def binAdd(s1, s2):
if not s1 or not s2:
return ''
maxlen = max(len(s1), len(s2))
s1 = s1.zfill(maxlen)
s2 = s2.zfill(maxlen)
result = ''
carry = 0
i = maxlen - 1
while(i >= 0):
s = int(s1[i]) + int(s2[i])
if s == 2: #1+1
if carry == 0:
carry = 1
result = "%s%s" % (result, '0')
else:
result = "%s%s" % (result, '1')
elif s == 1: # 1+0
if carry == 1:
result = "%s%s" % (result, '0')
else:
result = "%s%s" % (result, '1')
else: # 0+0
if carry == 1:
result = "%s%s" % (result, '1')
carry = 0
else:
result = "%s%s" % (result, '0')
i = i - 1;
if carry>0:
result = "%s%s" % (result, '1')
return result[::-1]
Can be simple if you parse the strings by int (shown in the other answer). Here is a kindergarten-school-math way:
>>> def add(x,y):
maxlen = max(len(x), len(y))
#Normalize lengths
x = x.zfill(maxlen)
y = y.zfill(maxlen)
result = ''
carry = 0
for i in range(maxlen-1, -1, -1):
r = carry
r += 1 if x[i] == '1' else 0
r += 1 if y[i] == '1' else 0
# r can be 0,1,2,3 (carry + x[i] + y[i])
# and among these, for r==1 and r==3 you will have result bit = 1
# for r==2 and r==3 you will have carry = 1
result = ('1' if r % 2 == 1 else '0') + result
carry = 0 if r < 2 else 1
if carry !=0 : result = '1' + result
return result.zfill(maxlen)
>>> add('1','111')
'1000'
>>> add('111','111')
'1110'
>>> add('111','1000')
'1111'
It works both ways
# as strings
a = "0b001"
b = "0b010"
c = bin(int(a, 2) + int(b, 2))
# as binary numbers
a = 0b001
b = 0b010
c = bin(a + b)
you can use this function I did:
def addBinary(self, a, b):
"""
:type a: str
:type b: str
:rtype: str
"""
#a = int('10110', 2) #(0*2** 0)+(1*2**1)+(1*2**2)+(0*2**3)+(1*2**4) = 22
#b = int('1011', 2) #(1*2** 0)+(1*2**1)+(0*2**2)+(1*2**3) = 11
sum = int(a, 2) + int(b, 2)
if sum == 0: return "0"
out = []
while sum > 0:
res = int(sum) % 2
out.insert(0, str(res))
sum = sum/2
return ''.join(out)
def addBinary(self, A, B):
min_len, res, carry, i, j = min(len(A), len(B)), '', 0, len(A) - 1, len(B) - 1
while i>=0 and j>=0:
r = carry
r += 1 if A[i] == '1' else 0
r += 1 if B[j] == '1' else 0
res = ('1' if r % 2 == 1 else '0') + res
carry = 0 if r < 2 else 1
i -= 1
j -= 1
while i>=0:
r = carry
r += 1 if A[i] == '1' else 0
res = ('1' if r % 2 == 1 else '0') + res
carry = 0 if r < 2 else 1
i -= 1
while j>=0:
r = carry
r += 1 if B[j] == '1' else 0
res = ('1' if r % 2 == 1 else '0') + res
carry = 0 if r < 2 else 1
j -= 1
if carry == 1:
return '1' + res
return res
#addition of two binary string without using 'bin' inbuilt function
numb1 = input('enter the 1st binary number')
numb2 = input("enter the 2nd binary number")
list1 = []
carry = '0'
maxlen = max(len(numb1), len(numb2))
x = numb1.zfill(maxlen)
y = numb2.zfill(maxlen)
for j in range(maxlen-1,-1,-1):
d1 = x[j]
d2 = y[j]
if d1 == '0' and d2 =='0' and carry =='0':
list1.append('0')
carry = '0'
elif d1 == '1' and d2 =='1' and carry =='1':
list1.append('1')
carry = '1'
elif (d1 == '1' and d2 =='0' and carry =='0') or (d1 == '0' and d2 =='1' and
carry =='0') or (d1 == '0' and d2 =='0' and carry =='1'):
list1.append('1')
carry = '0'
elif d1 == '1' and d2 =='1' and carry =='0':
list1.append('0')
carry = '1'
else:
list1.append('0')
if carry == '1':
list1.append('1')
addition = ''.join(list1[::-1])
print(addition)
Not an optimal solution but a working one without use of any inbuilt functions.
# two approaches
# first - binary to decimal conversion, add and then decimal to binary conversion
# second - binary addition normally
# binary addition - optimal approach
# rules
# 1 + 0 = 1
# 1 + 1 = 0 (carry - 1)
# 1 + 1 + 1(carry) = 1 (carry -1)
aa = a
bb = b
len_a = len(aa)
len_b = len(bb)
min_len = min(len_a, len_b)
carry = 0
arr = []
while min_len > 0:
last_digit_aa = int(aa[len(aa)-1])
last_digit_bb = int(bb[len(bb)-1])
add_digits = last_digit_aa + last_digit_bb + carry
carry = 0
if add_digits == 2:
add_digits = 0
carry = 1
if add_digits == 3:
add_digits = 1
carry = 1
arr.append(add_digits) # will rev this at the very end for output
aa = aa[:-1]
bb = bb[:-1]
min_len -= 1
a_len_after = len(aa)
b_len_after = len(bb)
if a_len_after > 0:
while a_len_after > 0:
while carry == 1:
if len(aa) > 0:
sum_digit = int(aa[len(aa) - 1]) + carry
if sum_digit == 2:
sum_digit = 0
carry = 1
arr.append(sum_digit)
aa = aa[:-1]
else:
carry = 0
arr.append(sum_digit)
aa = aa[:-1]
else:
arr.append(carry)
carry = 0
if carry == 0 and len(aa) > 0:
arr.append(aa[len(aa) - 1])
aa = aa[:-1]
a_len_after -= 1
if b_len_after > 0:
while b_len_after > 0:
while carry == 1:
if len(bb) > 0:
sum_digit = int(bb[len(bb) - 1]) + carry
if sum_digit == 2:
sum_digit = 0
carry = 1
arr.append(sum_digit)
bb = bb[:-1]
else:
carry = 0
arr.append(sum_digit)
bb = bb[:-1]
else:
arr.append(carry)
carry = 0
if carry == 0 and len(bb) > 0:
arr.append(bb[len(bb) - 1])
bb = bb[:-1]
b_len_after -= 1
if carry == 1:
arr.append(carry)
out_arr = reversed(arr)
out_str = "".join(str(x) for x in out_arr)
return out_str
I am making some practice code for a game similar to the board game, MasterMind-- and It keeps coming out with this error, and I can't figure out why it's doin it. Here's the code:
def Guess_Almost (Guess, Answer):
a = ''.join([str(v) for v in Answer])
g = str(Guess)
n = 0
am = 0
while n < 5:
if g[n] == a[0]:
am = am + 1
if g[n] == a[2]:
am = am + 1
if g[n] == a[3]:
am = am + 1
if g[n] == a[3]:
am = am + 1
n = n + 1
return(am)
Okay, the Guess is specified to be 4 integers, and the Answer is a list containing 4 numbers. They both have the same 'len' after the code, so i don't have a clue.
The point of this code is to turn the Answer into a string of 4 numbers, and see if any of those numbers match thoise of the guess, and return how many total matches there are.
See if this helps
def Guess_Almost (Guess, Answer):
a = ''.join([str(v) for v in Answer])
g = str(Guess)
n = 0
am = 0
if len(g) >= 5 and len(a) >=4:
while n < 5:
if g[n] == a[0]:
am = am + 1
if g[n] == a[2]:
am = am + 1
if g[n] == a[3]:
am = am + 1
if g[n] == a[3]:
am = am + 1
n = n + 1
return(am)