Approach

1. Prefix and suffix sums:

2. Use a prefix sum array to calculate the sum of the first i + 1 elements.

3. Use the total sum of the array to calculate the suffix sum dynamically: $suffixSum = totalSum - prefixSum$.

4. Check valid Splits:

5. Iterate through the array from index 0 to n-2.

6. For each i, check if: $$prefixSum \ge suffixSum$$ equivalent to: $$2 * prefixSum \ge totalSum$$

7. Count valid Splits:

8. Increment the count whenever the above condition is true.

Complexity

• Time complexity: O(N) where N is the length of the given array.

• Space complexity: O(1) extra space.

Code

Go

func waysToSplitArray(nums []int) int {
    ans, n, totalSum := 0, len(nums), 0
    for _, num := range nums {
        totalSum += num
    }
    sum := 0
    for i := 0; i < n - 1; i++ {
        sum += nums[i]
        if 2 * sum >= totalSum {
            ans++
        }
    }
    return ans
}

Rust

impl Solution {
    pub fn ways_to_split_array(nums: Vec<i32>) -> i32 {
        let n = nums.len();
        let mut ans = 0;
        let total_sum = nums.iter().fold(0i64, |acc, &val| acc + val as i64);
        nums
          .into_iter()
          .take(n - 1)
          .scan(0, |s, num| {
            *s += num as i64;
            Some(if *s >= total_sum - *s {1} else {0})
          }).sum()
    }
}