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https://repl.it/C8Cl/1 created by charles2588
#Find product of all other numbers in the array for a given index except the number at that index.for ex. [1,2,3] = [6(3*2),3(1*3),2(1*2)]
def multiplier(arr):
result=[1 for i in arr]
#Brute force
for i in range(len(arr)):
for j in range(len(arr)):
if j==i:
continue
else:
result[i]=result[i]*arr[j]
return result
def multiplier2(arr):
#Greedy to avoid multipying same numbers again.
#find products before each index and progressing towards the end and put it in an array
productbeforeeachindex=[1]*len(arr)
currentproduct=1
i=0
while(i<len(arr)):
productbeforeeachindex[i]*=currentproduct
currentproduct*=arr[i]
i+=1
#find products after each index by starting at end and going back towards the start and put it in an array
productaftereachindex=[1]*len(arr)
currentproduct=1
j=len(arr)-1
while(j>=0):
productaftereachindex[j]*=currentproduct
currentproduct*=arr[j]
j-=1
#at each index...multipy (product before and after that index)
productexceptatindex=[None]*len(arr)
for i in range(len(productexceptatindex)):
productexceptatindex[i]=productbeforeeachindex[i]*productaftereachindex[i]
return productexceptatindex
def multiplier3(arr):
#find products before each index and progressing towards the end and put it in an array
productbeforeeachindex=[1]*len(arr)
currentproduct=1
i=0
while(i<len(arr)):
productbeforeeachindex[i]=currentproduct
currentproduct*=arr[i]
i+=1
#find products after each index by starting at end and going back towards the start and put it in an array
productexceptatindex=[1]*len(arr)
currentproduct=1
j=len(arr)-1
while(j>=0):
productexceptatindex[j]=productbeforeeachindex[j]*currentproduct
currentproduct*=arr[j]
j-=1
return productexceptatindex
print(multiplier([2, 7, 3, 4]))
print(multiplier([3, 0, 3, 4]))
print(multiplier2([2, 7, 3, 4]))
print(multiplier3([2, 7, 3, 4]))
Python 3.5.1 (default, Dec 2015, 13:05:11)
[GCC 4.8.2] on linux
>>> [84, 24, 56, 42]
[0, 36, 0, 0]
[84, 24, 56, 42]
[84, 24, 56, 42]
=> None
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