Watch 10 video solutions for Find the Middle Index in Array, a easy level problem involving Array, Prefix Sum. This walkthrough by NeetCode has 413,348 views views. Want to try solving it yourself? Practice on FleetCode or read the detailed text solution.
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
Note: This question is the same as 724: https://leetcode.com/problems/find-pivot-index/