pivot index 3 solutions

LeetCode

Author: SanjarH

pivot.py

@@ -0,0 +1,91 @@
+# Learn Python together
+
+"""Given an array of integers nums, 
+calculate the pivot index of this array.
+The pivot index is the index where the sum of all the numbers
+strictly to the left of the index is equal to the sum of all 
+the numbers strictly to the index's right."""
+
+# Solution 1
+
+def pivotIndex1(nums) -> int:
+    pivot = 0
+    # getting sum of the numbers from left side of the pivot
+    left_sum = sum(nums[:pivot])
+    # getting sum of the numbers from fight side of the  pivot
+    right_sum = sum(nums[pivot+1:])
+    
+    # lopping through the list
+    for _ in range(len(nums)-1):
+        if left_sum == right_sum:
+            # if sums are equal, return the pivot index
+            return pivot  
+        else:
+            # otherwise left sum += pivot index, 
+            # right sum -= pivot index+1
+            left_sum += nums[pivot] 
+            right_sum -= nums[pivot+1] 
+            pivot += 1
+    # if the sums still not equal, return -1
+    if left_sum == right_sum:
+        return pivot
+    else:
+        return -1
+
+
+# Solution 2
+def pivotIndex2(nums) -> int:
+    left_sum = 0
+    # sum of all numbers
+    right_sum = sum(nums)
+
+    for i in range(len(nums)):
+        # substract the current num from right sum
+        right_sum -= nums[i] 
+        # return index if sums are equal
+        if left_sum == right_sum:
+            return i
+        # adding current num to the left sum
+        left_sum += nums[i] 
+    # if there isn't pivot, -1    
+    return -1
+        
+
+# Solution 3
+def pivotIndex3(nums) -> int:
+    left_sum = 0
+    # sum of all numbers
+    right_sum = sum(nums)
+
+    for i, num in enumerate(nums):
+        # if sums are equal, return index
+        if left_sum == right_sum -left_sum - num:
+            return i
+        # add current num to the left sum
+        left_sum += nums[i] 
+    # if there isn't pivot, -1
+    return -1
+        
+# check         
+nums = [1,7,3,6,5,6]
+nums2 = [1,7]
+print(pivotIndex1(nums)) # Output-> 3
+print(pivotIndex2(nums)) # Output-> 3
+print(pivotIndex3(nums)) # Output-> 3
+
+print(pivotIndex1(nums2)) # Output-> -1
+print(pivotIndex2(nums2)) # Output-> -1
+print(pivotIndex3(nums2)) # Output-> -1
+
+# Check time 
+import timeit
+
+t1 = timeit.timeit(lambda: pivotIndex1(nums), number=10000)
+print("pivotIndex1 execution time:", t1) # -> 0.011717599999999995
+
+t2 = timeit.timeit(lambda: pivotIndex2(nums), number=100000)
+print("pivotIndex2 execution time:", t2) # -> 0.08669160000000001
+
+t3 = timeit.timeit(lambda: pivotIndex3(nums), number=100000)
+print("pivotIndex3 execution time:", t3) # -> 0.09343009999999999
+