How can I search for the three maximum elements of a list and replace it at same index with its result when divided by 2.
Please what am I doing wrong:
input is: 2 5 8 19 1 15 7 20 11
output should be : 2 5 8 9.5 1 7.5 7 10 11
Index out of range is the result displayed
def numberInput(line):
lineInput = [int(i) for i in line.split()]
min1 = min(lineInput)
for j in range(len(lineInput)):
if lineInput[j]>min1 and lineInput[j] > lineInput[j+1]:
max1 = lineInput[j]/float(2)
else:
max1 = lineInput[j]/float(2)
lineInput[j] = max1
lineInput[j] = max1
return(lineInput)
number = '2 5 8 19 1 15 7 20 11'
print(numberInput(number))
If the order of list isn't important, you can simply sort the list in descending order and then replace the first 3 elements as
a = [2, 5, 8, 19, 1, 15, 7, 20, 11]
a.sort(reverse = True)
a[0] = a[0] / 2
a[1] = a[1] / 2
a[2] = a[2] / 2
Output
[10.0, 9.5, 7.5, 11, 8, 7, 5, 2, 1]
If the order is important,
import heapq
largest = heapq.nlargest(3, a)
for i in range(len(a)):
if a[i] in largest:
a[i] = a[i] / 2
Output
[2, 5, 8, 9.5, 1, 7.5, 7, 10.0, 11]
heapq.nlargest()
is a function of heapq which can give you n largest numbers from a list. Since lists in Python do not have a replace function, the list had to be traversed once, and then replaced manually. Hope this resolves your issue.
Why wouldn't you just walk through the list once (it maybe a bit longer code, but definitely efficient)
def numberInput(line):
lineInput = [int(i) for i in line.split()]
n = len(lineInput)
if n <= 3:
return [i / 2 for i in lineInput]
max_pairs = [(lineInput[i], i) for i in range(3)] # keep track of 3 max's and their indices
max_pairs.sort(key = lambda x: -x) # sort in descending order
for i in range(3, n):
if lineInput[i] >= max_pairs[0][0]: # greater than the largest element
max_pairs = [(lineInput[i], i)] + max_pairs[:2]
elif lineInput[i] >= max_pairs[1][0]: # greater than second element
max_pairs = [max_pairs[0], (lineInput[i], i), max_pairs[1]]
elif lineInput[i] >= max_pairs[2][0]: # greater than third element
max_pairs = max_pairs[:2] + [(lineInput[i], i)]
for pair in max_pairs:
lineInput[pair[1]] = lineInput[pair[0]] / 2
return lineInput
Explanation: max_pairs
is a set of three tuples, containing the maximum three elements and their indices
Note: I think the above is easiest to understand, but you can do it in a loop if you don't like all those ifs
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