Ways to split array into good subarrays

Array Math Dynamic Programming

34.8% acceptance

Feb 25, 2026

469

You are given a binary array nums. A subarray of an array is good if it contains exactly one element with the value 1. Return an integer denoting the number of ways to split the array nums into good subarrays. As the number may be too large, return it modulo 109 + 7. A subarray is a contiguous non-empty sequence of elements within an array.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn number_of_good_subarray_splits(nums: Vec<i32>) -> i32 {
    const MOD: i64 = 1_000_000_007;
    let mut ans: i64 = 1;
    let mut last_one: i64 = -1;
    let mut found = false;
    for (i, &v) in nums.iter().enumerate() {
      if v == 1 {
        if found {
          // gap between this 1 and last 1
          ans = (ans * (i as i64 - last_one)) % MOD;
        }
        found = true;
        last_one = i as i64;
      }
    }
    if !found { 0 } else { ans as i32 }
  }
}