LeetCode Entry

66. Plus One

01.01.2026 easy 2026 kotlin rust

Increment big number

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Problem TLDR

Increment big number #easy

Intuition

The simplest and robust solution is a separate container for result digits and a counter for carry.

Approach

• optimization: stop at first non-nine
• optimization: count suffix nines in a forward cache-friendly pass

  Complexity

• Time complexity: \(O(n)\)
• Space complexity: \(O(n)\)

  Code

  // 0ms
    fun plusOne(d: IntArray): IntArray {
        for (i in d.size-1 downTo 0) if (d[i]<9) {++d[i]; return d} else d[i]=0
        return IntArray(d.size+1).also {it[0]=1}
    }
  

  // 0ms
    pub fn plus_one(mut d: Vec<i32>) -> Vec<i32> {
        let (mut c,n) = (0,d.len()); for &d in &d {if d < 9 {c=0} else {c+=1}}
        if c==n { let mut r = vec![0;c+1];r[0]=1; return r}
        d[n-c..n].fill(0); d[n-c-1] += 1; d
    }