doingmathwithpython · amitsaha · Jan 2, 2020 · Jan 2, 2020 · Jan 2, 2020
diff --git a/explorations/trailing_zeros/trailing_zeros.png b/explorations/trailing_zeros/trailing_zeros.png
diff --git a/explorations/trailing_zeros/trailing_zeros.py b/explorations/trailing_zeros/trailing_zeros.py
@@ -0,0 +1,43 @@
+# This program will print the number of trailing zeros the factorial
+# of a number
+# The formula and the associated explanations are available at:
+# https://brilliant.org/wiki/trailing-number-of-zeros/
+
+# Notes on the Python implementation are available on https://doingmathwithpython.github.io
+
+import math
+
+
+def is_positive_integer(x):
+    try:
+        x = float(x)
+    except ValueError:
+        return False
+    else:
+        if x.is_integer() and x > 0:
+            return True
+        else:
+            return False
+
+
+def trailing_zeros(num):
+    if is_positive_integer(num):
+        # The above function call has done all the sanity checks for us
+        # so we can just convert this into an integer here
+        num = int(num)
+
+        k = math.floor(math.log(num, 5))
+        zeros = 0
+        for i in range(1, k + 1):
+            zeros = zeros + math.floor(num/math.pow(5, i))
+        return zeros 
+    else:
+        print("Factorial of a non-positive non-integer is undefined")
+
+
+if __name__ == "__main__":
+    fact_num = input(
+        "Enter the number whose factorial's trailing zeros you want to find: "
+    )
+    num_zeros = trailing_zeros(fact_num)
+    print("Number of trailing zeros: {0}".format(num_zeros))
diff --git a/explorations/trailing_zeros/trailing_zeros_plot.py b/explorations/trailing_zeros/trailing_zeros_plot.py
@@ -0,0 +1,48 @@
+# This program will print the number of trailing zeros the factorial
+# of a number
+# The formula and the associated explanations are available at:
+# https://brilliant.org/wiki/trailing-number-of-zeros/
+
+# Notes on the Python implementation are available on https://doingmathwithpython.github.io
+
+import math
+import matplotlib.pyplot as plt
+
+
+def is_positive_integer(x):
+    try:
+        x = float(x)
+    except ValueError:
+        return False
+    else:
+        if x.is_integer() and x > 0:
+            return True
+        else:
+            return False
+
+
+def trailing_zeros(num):
+    if is_positive_integer(num):
+        # The above function call has done all the sanity checks for us
+        # so we can just convert this into an integer here
+        num = int(num)
+
+        k = math.floor(math.log(num, 5))
+        zeros = 0
+        for i in range(1, k + 1):
+            zeros = zeros + math.floor(num/math.pow(5, i))
+        return zeros 
+    else:
+        print("Factorial of a non-positive integer is undefined")
+
+
+if __name__ == "__main__":
+    num_range = range(5, 10000, 10)
+    zeros = []
+    for num in num_range:
+        num_zeros = trailing_zeros(num)
+        zeros.append(num_zeros)
+    for x, y in zip(num_range, zeros):
+        print(x,y)
+    plt.plot(num_range, zeros)
+    plt.savefig('trailing_zeros.png')