leetcode/findMiddleIndex.py at master · Kymoraa/leetcode · GitHub

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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.
"""


class Solution:
    def findMiddleIndex(self, nums: list[int]) -> int:
        left_sum = 0
        right_sum = sum(nums)

        for i in range(len(nums)):
            right_sum -= nums[i]
            if left_sum == right_sum:
                return i
            left_sum += nums[i]

        return -1