LeetCode Entry

2206. Divide Array Into Equal Pairs

17.03.2025 easy 2025 kotlin rust

All numbers in pairs

2206. Divide Array Into Equal Pairs easy blog post substack youtube

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Problem TLDR

All numbers in pairs #easy #counting #sorting

Intuition

Many ways:

• HashMap
• counting, we have at most 500 elements each at most 500
• sorting, can help to save memory
• BitSet, we only have to track parity bit

Approach

• implement all
• we can round-wrap bitset into a single 64-bit value, as test-cases are passing right now (but can fail for two bits overlapping from different numbers)

Complexity

• Time complexity: \(O(n)\), or O(nlog(n)) for sort

• Space complexity: \(O(n)\), or O(1) for sort

Code

    fun divideArray(nums: IntArray) = nums
        .sorted().chunked(2).all { it[0] == it[1] }

``kotlin

fun divideArray(nums: IntArray) = nums
    .groupBy { it }.all { it.value.size % 2 < 1 }

```rust

    pub fn divide_array(mut n: Vec<i32>) -> bool {
        n.sort();
        n.chunk_by(|a, b| a == b).all(|c| c.len() % 2 < 1)
    }

    pub fn divide_array(nums: Vec<i32>) -> bool {
        let mut f = vec![0; 501];
        for x in nums { f[x as usize] ^= 1; f[0] += f[x as usize] * 2 - 1 }
        f[0] < 1
    }

    bool divideArray(vector<int>& n) {
        int f[501];
        for (int x: n) *f += (f[x] ^= 1) * 2 - 1;
        return !*f;
    }

    bool divideArray(vector<int>& n) {
        bitset<501> f;
        for (int x: n) f[x] = !f[x];
        return !f.any();
    }

    bool divideArray(vector<int>& n) {
        long long f = 0;
        for (int x: n) f ^= 1LL << (x % 64);
        return !f;
    }