bitwise

interview_cake/binary_search.py

@@ -0,0 +1 @@
+#!/usr/bin/env python

interview_cake/bitwise_stuff/clean_bit.py

@@ -0,0 +1,35 @@
+#!/usr/bin/python
+
+''' Clear a bit in a binary number.
+    Like the reverse of set bit:
+    1) first create a number filled of 1s,
+        with 0 at i (can create 0001000 and ~)
+    2) AND the number so it clears the ith bit
+'''
+
+
+
+def clear_bit(num, i):
+    mask = ~ (1 << i)   # -0b10001
+    return bin(num & mask)
+
+
+def clear_all_bits_from_i_to_0(num, i):
+    mask = ~ ( (1 << (i+1)) - 1)
+    return bin(num & mask)
+
+
+def clear_all_bits_from_most_sig_to_1(num, i):
+    mask =  ( 1 << i) -1
+    return bin(num & mask)
+
+
+if __name__ == '__main__':
+    num = int('10010000', 2)
+    print clear_bit(num, 4)   # '0b10000000'
+
+    num = int('10010011', 2)
+    print clear_all_bits_from_i_to_0(num, 2)  # '0b10010000'
+
+    num = int('1110011', 2)
+    print clear_all_bits_from_most_sig_to_1(num, 2)  #'0b11'

interview_cake/bitwise_stuff/count_bits.py

@@ -0,0 +1,37 @@
+#!/usr/bin/python
+
+''' This method returns the number of bits that are necessary to change to convert two
+    numbers A and B:
+    1) XOR
+    2) count 1s
+'''
+
+def count_bits_swap2(a, b):
+    count = 0
+    m = a^b
+    while m:
+        count +=1
+        m = m & (m-1)
+    return count
+
+
+
+def count_bits_swap(a, b):
+    m = a^b
+    return count_1s(m)
+
+
+def count_1s(m):
+    count = 0
+    while m:
+        if m& 1 :
+            count +=1
+        m >>= 1
+    return count
+
+
+if __name__ == '__main__':
+    a = int('10010000', 2)
+    b = int('01011010', 2)
+    print count_bits_swap(a, b)  #4
+    print count_bits_swap2(a, b)  #4

interview_cake/bitwise_stuff/get_bit.py

@@ -0,0 +1,20 @@
+#!/usr/bin/python
+''' Set a bit in a binary number:
+    1) Shifts 1 over by i bits
+    2) make an OR with the number, only the value at bit i will change and all the others bit
+    of the mask are zero so will not affect the num
+
+'''
+def set_bit(num, i):
+    mask = 1 << i
+    return bin( num | mask )
+
+
+if __name__ == '__main__':
+    num = int('0100100', 2)
+    print set_bit(num, 0)   #'0b100101'
+    print set_bit(num, 1)   #'0b100110'
+    print set_bit(num, 2)   # nothing change '0b100100'
+    print set_bit(num, 3)   #'0b101100'
+    print set_bit(num, 4) #'0b110100'
+    print set_bit(num, 5)     # nothing change '0b100100'

interview_cake/bitwise_stuff/update_bit.py

@@ -0,0 +1,19 @@
+#!/usr/bin/python
+
+''' This method merges set bit and clean bit:
+    1) first clear the bit at i using a mask such as 1110111
+    2) then shift the intended value v by i bits
+    3) this will create a number with bit i to v and all other to 0
+    4) finally update the ith bit with or
+'''
+
+
+
+def  update_bit(num, i, v):
+    mask = ~ (1 << i)
+    return bin( (num & mask) | (v << i) )
+
+
+if __name__ == '__main__':
+    num = int('10010000', 2)
+    print update_bit(num, 2, 1)   # '0b10010100'

interview_cake/float_bin_num.py

@@ -0,0 +1,26 @@
+#!/usr/bin/python
+
+''' Given a real number between 0 and 1 (eg: 0.72), this method print the binary
+    representation. If the Number cannot be represented accurately in binary, with at
+    most 32 chars, print error:
+'''
+
+def get_float_rep(num):
+    if num >= 1 or num <= 0: return 'Error 1'
+    result = '.'
+    while num:
+        if len(result) >= 32: return 'Error 2', result
+        r = num*2
+        if r >= 1:
+            result += '1'
+            num = r - 1
+        else:
+            result += '0'
+            num = r
+    return result
+
+
+if __name__ == '__main__':
+    print get_float_rep(0.72) #('Error 2', '.1011100001010001111010111000010')
+    print get_float_rep(0.1) # ('Error 2', '.0001100110011001100110011001100')
+    print get_float_rep(0.5) #'.1'

interview_cake/merge_sorted_list.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python
+
 """
 In order to win the prize for most cookies sold, my friend Alice and 
 # I are going to merge our Girl Scout Cookies orders and enter as one unit.

interview_cake/palindrome.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python
+
 """
 Write an efficient function that checks whether 
 any permutation of an input string is a palindrome.

interview_cake/reverse_in_place.py

@@ -1,5 +1,9 @@
-# Write a function that takes a list of characters and reverses the letters in place.
-# O(n) time and O(1)O(1) space.
+#!/usr/bin/env python
+
+"""
+Write a function that takes a list of characters and reverses the letters in place.
+O(n) time and O(1)O(1) space.
+"""
 
 def reverse_in_place(char_list):
     return char_list[::-1]