# 19.02.2026 [696. Count Binary Substrings]
Count substrings of *01* and *10* #easy #sliding_window
19.02.2026
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Problem TLDR
Count substrings of 01 and 10 #easy #sliding_window
Intuition
Count consequent zeros and ones. Slide pair-wise res += min(prev, curr).
Approach
the fun solution is to split the string
itertools in Rust allow nested windows without vec allocation
Complexity
Time complexity: $$O(n)$$
Space complexity: $$O(1)$$
Code
// 69ms
fun countBinarySubstrings(s: String) = s
.replace("01", "0 1").replace("10", "1 0").split(" ")
.zipWithNext { a, b -> min(a.length, b.length)}.sum()
// 0ms
pub fn count_binary_substrings(s: String) -> i32 {
s.as_bytes().chunk_by(|a,b|a==b).map(|c|c.len() as i32)
.tuple_windows().map(|(a,b)|a.min(b)).sum()
}