﻿ Python: Find the single element appears once in a list where every element appears four times except for one - w3resource

# Python Challenges: Find the single element appears once in a list where every element appears four times except for one.

## Python Challenges - 1: Exercise-14 with Solution

Write a Python program to find the single element appears once in a list where every element appears four times except for one.

Sample Solution:-

Python Code:

``````class Solution_once:
def singleNumber(self, arr):
ones, twos = 0, 0
for x in arr:
ones, twos = (ones ^ x) & ~twos, (ones & x) | (twos & ~x)
assert twos == 0
return ones
class Solution_twice:
def single_number(arr):
ones, twos, threes = 0, 0, 0
for x in arr:
ones, twos, threes = (~x & ones) | (x & ~ones & ~twos & ~threes), (~x & twos) | (x & ones), (~x & threes) | (x & twos)
return twos

if __name__ == "__main__":
print(Solution_once().singleNumber([1, 1, 1, 2, 2, 2, 3]))
print(Solution_once().singleNumber([5, 3, 0, 3, 5, 5, 3]))
```
```

Sample Output:

```3
0
```

Flowchart:

Python Code Editor:

```class Solution_once:
def singleNumber(self, arr):
ones, twos = 0, 0
for x in arr:
ones, twos = (ones ^ x) & ~twos, (ones & x) | (twos & ~x)
assert twos == 0
return ones
class Solution_twice:
def single_number(arr):
ones, twos, threes = 0, 0, 0
for x in arr:
ones, twos, threes = (~x & ones) | (x & ~ones & ~twos & ~threes), (~x & twos) | (x & ones), (~x & threes) | (x & twos)
return twos

if __name__ == "__main__":
print(Solution_once().singleNumber([1, 1, 1, 2, 2, 2, 3]))
print(Solution_once().singleNumber([5, 3, 0, 3, 5, 5, 3]))```

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