fifo

Author: jordanpaulchan

fifo/description.md

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+# FIFO data structure
+
+Implement a FIFO (first in, first out) data struture with O(1) push and O(1) pop operations, without using a libary or native implementation.
+
+Given n sequential add and get operations, perform each operation in order.
+
+## Example
+
+### Input:
+
+put 1
+put 2
+put 3
+pop
+pop
+pop
+
+### Output:
+
+1
+2
+3
+
+## Run the program
+
+In the folder run the command:
+
+```
+python fifo.py
+```

fifo/fifo.py

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+import unittest
+
+
+class FIFO:
+ def __init__(self, size=5):
+ self.list = [0] * size
+ self.push_idx = 0
+ self.pop_idx = 0
+
+ def push(self, val):
+ self.list[self.push_idx] = val
+ self.push_idx = (self.push_idx + 1) % len(self.list)
+
+ if self.push_idx == self.pop_idx:
+ self.increase_lst_size()
+
+ def pop(self):
+ if self.pop_idx == self.push_idx:
+ return None
+
+ val = self.list[self.pop_idx]
+ self.pop_idx = (self.pop_idx + 1) % len(self.list)
+
+ return val
+
+ def increase_lst_size(self):
+ new_list = [0] * (len(self.list) * 2)
+ new_list_idx = 0
+
+ for i in xrange(0, len(self.list)):
+ idx = (self.push_idx + i) % len(self.list)
+ new_list[new_list_idx] = self.list[idx]
+ new_list_idx += 1
+
+ self.list = new_list
+ self.push_idx = new_list_idx
+ self.pop_idx = 0
+
+
+class FIFOTests(unittest.TestCase):
+ def test_push_pop(self):
+ fifo = FIFO()
+ fifo.push(1)
+ self.assertEqual(fifo.pop(), 1)
+
+ def test_increase_size(self):
+ fifo = FIFO(2)
+ fifo.push(1)
+ fifo.push(2)
+ self.assertEqual(len(fifo.list), 4)
+
+ def test_wrap(self):
+ fifo = FIFO(3)
+ fifo.push(1)
+ fifo.push(2)
+ fifo.pop()
+ fifo.pop()
+ fifo.push(3)
+ fifo.push(4)
+ self.assertEqual(len(fifo.list), 3)
+ self.assertEqual(fifo.pop(), 3)
+ self.assertEqual(fifo.pop(), 4)
+
+
+if __name__ == '__main__':
+ unittest.main()