Add Power set of a given set Algorithm

Author: th92rodr

google_interview_prep/power_set_of_a_given_set.py

@@ -0,0 +1,64 @@
+'''
+Print all subsets (power set) of a given set
+
+The input for this problem will be an array of numbers representing a set, which only contains unique numbers,
+and your goal is to print every possible set combination, otherwise known as the power set.
+
+For example:
+input set = [1, 2, 3]
+power set = [ [], [1], [2], [3], [1, 2], [2, 3], [1, 3] [1, 2, 3] ]
+
+The power set contains every possible combination of numbers.
+It also includes the empty set which contains no numbers from the original set.
+
+https://coderbyte.com/algorithm/print-all-subsets-given-set
+'''
+
+
+'''
+There will be 2N possible combinations of a set of length N,
+because every element can either be in the set or not, which gives us 2 possibilities,
+and we do this for N numbers, giving us 2 * 2 * 2 ... = 2^N.
+
+(1) Loop from 0 to 2^N
+(2) For each number get the binary representation of the number, example: 3 = 011
+(3) Determine from the binary representation whether or not to include a number from the set, example: 011 = [exclude, include, include]
+'''
+def power_set(set):
+    response = []
+
+    # loop from 0 to 2^N
+    for x in range(0, pow(2, len(set))):
+        print('\nnumber:', x, '|| binary:', bin(x))
+
+        # get the binary representation of the number
+        # and put each digit in a list position
+        binary = list(bin(x))
+
+        # delete the first two characters which are '0b'
+        del binary[0:2]
+
+        # fill the list with left zeros
+        # padding the binary number so 1 becomes 001 for example
+        while len(binary) < len(set):
+            binary.insert(0, 0)
+
+        # convert all the elements to integers
+        binary = list(map(int, binary))
+        print('binary list:', binary)
+
+        # determine from the binary representation whether or not to include a number from the set
+        # building the combination that matches the 1's in the binary number
+        res = []
+        for index in range(len(binary)):
+            if (binary[index]):
+                res.append(set[index])
+
+        # add the new combination to the response
+        response.append(res)
+
+    response.sort()
+    return response
+
+
+print(' Input Set: [1, 2, 3]\n Output:', power_set([1, 2, 3]))