LeetCode Entry

3754. Concatenate Non-Zero Digits and Multiply by Sum I

07.07.2026 easy 2026 kotlin rust

Sum digits concat digits

3754. Concatenate Non-Zero Digits and Multiply by Sum I easy substack youtube

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Problem TLDR

Sum digits * concat digits

Intuition

Sum them and concat them with strings. Or go from tail with match.

Approach

• can be done in two phases for shorter code

Complexity

• Time complexity: \(O(logn)\)

• Space complexity: \(O(logn)\)

Code

    fun sumAndMultiply(n: Int) =
    ("0"+"$n".filter{it>'0'}).toLong()*"$n".sumOf{it-'0'}

    pub fn sum_and_multiply(mut n: i32) -> i64 {
        let(mut v,mut s,mut m)=(0,0,1);
        while n>0{let d=(n%10)as i64;s+=d;if d>0{v+=d*m;m*=10}n/=10}v*s
    }