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.

LeetCode Problem - 1991

class Solution {
    // Method to find the middle index in the given array
    public int findMiddleIndex(int[] nums) {
        int len = nums.length; // Get the length of the array
        int[] sumLeft =  new int[len]; // Array to store the sum of elements to the left of each index
        int[] sumRight = new int[len]; // Array to store the sum of elements to the right of each index

        // Calculate the sum of elements to the left of each index
        sumLeft[0] = nums[0];
        int flag = nums[0];
        for(int i = 1; i < len; i++){
            flag += nums[i];
            sumLeft[i] = flag;
        }

        // Calculate the sum of elements to the right of each index
        sumRight[len - 1] = nums[len - 1];
        flag = nums[len - 1];
        for(int i = len - 2; i >= 0; i--){
            flag += nums[i];
            sumRight[i] = flag;
        }

        // Check at which index sumRight[i] and sumLeft[i] are equal and return
        for(int i = 0; i < len; i++){
            if(sumRight[i] == sumLeft[i]) return i;
        }

        // If no middle index is found, return -1
        return -1;
    }
}