Find the Middle Index in Array

Author: nirmalnishant645

1991-Find-the-Middle-Index-in-Array.py

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+'''
+Given a 0-indexed integer array nums, find the leftmost middleIndex (i.e., the smallest amongst all the possible ones).
+A middleIndex is an index where nums[0] + nums[1] + ... + nums[middleIndex-1] == nums[middleIndex+1] + nums[middleIndex+2] + ... + nums[nums.length-1].
+If middleIndex == 0, the left side sum is considered to be 0. Similarly, if middleIndex == nums.length - 1, the right side sum is considered to be 0.
+Return the leftmost middleIndex that satisfies the condition, or -1 if there is no such index.
+
+Example 1:
+Input: nums = [2,3,-1,8,4]
+Output: 3
+Explanation: The sum of the numbers before index 3 is: 2 + 3 + -1 = 4
+The sum of the numbers after index 3 is: 4 = 4
+
+Example 2:
+Input: nums = [1,-1,4]
+Output: 2
+Explanation: The sum of the numbers before index 2 is: 1 + -1 = 0
+The sum of the numbers after index 2 is: 0
+
+Example 3:
+Input: nums = [2,5]
+Output: -1
+Explanation: There is no valid middleIndex. 
+
+Constraints:
+1 <= nums.length <= 100
+-1000 <= nums[i] <= 1000
+'''
+
+class Solution:
+ def findMiddleIndex(self, nums: List[int]) -> int:
+ left_sum = 0
+ right_sum = sum(nums)
+ 
+ for i, num in enumerate(nums):
+ if left_sum == right_sum - num:
+ return i
+ 
+ left_sum += num
+ right_sum -= num
+ 
+ return -1