finding new date after subtracting certain months in given date

Author: NirmalSilwal

Jash Data Science interview/challenge1.py

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+
+
+"""
+implement function 'subtract_months' to subtract 'n' number of months from a given year and month.
+
+Inputs: Is a list of tuples [(year1, month1, months_to_subtract1), (year2, month2, months_to_subtract2), ...] 
+where, year is a 4 digit integer
+month is an interger value between 1 to 12, 1=January, 2=February, ... 12=December) and 
+months_to_subtract is an integer
+
+Output: Is a list of tuples [(result_year1, result_month1), (result_year2, result_month2), ...] 
+year (4 digit integer) month (interger value between 1 to 12, 1=January, 2=February, ... 12=December)
+
+For example: subtract 3 months from May 2020. This should result in an output Feb 2020
+In this example inputs: year=2020 month=5
+output: year=2020 month=2
+
+Code evaluation criteria:
+1. Correctness for all possible cases
+2. Code should be clean and readable
+3. optimal with respect to time and space complexity (e.g. avoid unnecessary extra variables and loops) 
+
+"""
+
+def subtract_months(input_list):
+    output_list = []
+    
+    #TODO: implement your code here
+    
+    for input_data in input_list:
+    
+        assert len(input_data) == 3
+
+        year = input_data[0]
+        month = input_data[1]
+        months_to_subtract = input_data[2]
+
+        if months_to_subtract > 12:
+            left_month = months_to_subtract - month
+
+            if left_month >= 12:
+
+                minus_year = left_month // 12
+                output_year = year - minus_year - 1
+                months_to_be_subtracted = left_month - (12 * minus_year)    
+                output_list.append((output_year, 12 - months_to_be_subtracted))
+
+            else:
+                output_list.append((year-1, 12 - left_month))
+
+        else:
+            if months_to_subtract < month:
+                output_month = month - months_to_subtract
+                output_list.append((year, output_month))
+
+            else:
+                output_year = year - 1
+                output_month = 12 - (months_to_subtract - month)
+                output_list.append((output_year, output_month))
+                
+    return output_list
+
+
+
+# subtract_months([(2020, 5, 3), (2020, 6, 7), (2020, 5, 30), (2020, 5, 15), (2020, 5, 8)])