Create products_of_all_ints.py

Author: learning-zone

products_of_all_ints.py

@@ -0,0 +1,123 @@
+def get_products_of_all_ints_except_at_index(lst):
+    """ Takes a list of integers and returns a list of the products except the integer at that index. Do not use division.
+
+    >>> get_products_of_all_ints_except_at_index([1, 7, 3, 4])
+    [84, 12, 28, 21]
+
+    >>> get_products_of_all_ints_except_at_index([1, 0, 3, 4])
+    [0, 12, 0, 0]
+    """
+
+    # Runtime: O(n^2)
+    # Spacetime: O(n^2)
+
+    products = []
+
+    for a in range(len(lst)):
+        product = 1
+
+        for b in range(len(lst)):
+            if a != b:
+                product *= lst[b]
+        products.append(product)
+
+    return products
+
+# Testing
+# a = 0
+# product = 1
+# b = 0
+# skip
+# b = 1
+# product = 1 * 7
+# b = 2
+# product = 1 * 7 * 3
+# b = 3
+# product = 1 * 7 * 3 * 4
+
+# products = [84]
+
+# a = 1
+# product = 7
+
+# b = 0
+# product = 7 * 1
+
+
+
+def get_products_of_all_ints_except_at_index_optimized(lst):
+    """ Takes a list of integers and returns a list of the products except the integer at that index. Do not use division.
+
+    >>> get_products_of_all_ints_except_at_index_optimized([1, 7, 3, 4])
+    [84, 12, 28, 21]
+
+    >>> get_products_of_all_ints_except_at_index_optimized([1, 0, 3, 4])
+    [0, 12, 0, 0]
+    """
+
+    # Runtime: O(n)
+    # Spacetime: O(n)
+
+    products = []
+    product = 1
+    product_reverse = 1
+    products_before = []
+    products_after = []
+
+    for i in range(len(lst)):
+        products_before.append(product)
+        product *= lst[i]
+
+    for i in range(len(lst)-1, -1, -1):
+        products_after.append(product_reverse)
+        product_reverse *= lst[i]
+
+    for i in range(len(products_before)):
+        products.append(products_after[-i-1] * products_before[i])
+
+    return products
+
+
+# Testing
+# lst = [1, 7, 3, 4]
+
+# first for loop
+# i = 0
+# products_before = [1]
+# product = 1
+# i = 1
+# products_before = [1, 1]
+# product = 7
+# i = 2
+# products_before = [1, 1, 7]
+# product = 21
+# i = 3
+# products_before = [1, 1, 7, 21]
+# product = 84
+# i = 4
+
+# second for loop
+# i = 3
+# products_after = [1]
+# product_reverse = 4
+# i = 2
+# products_after [1, 4]
+# product_reverse = 12
+# i = 1
+# products_after = [1, 4, 12]
+# product_reverse = 84
+# i = 0
+# products_after = [1, 4, 12, 84]
+# product_reverse = 84
+# i = -1
+
+
+
+
+if __name__ == '__main__':
+    import doctest
+    results = doctest.testmod()
+
+    if results.failed == 0:
+        print "ALL TESTS PASSED"
+