LeetCode Entry

1536. Minimum Swaps to Arrange a Binary Grid

02.03.2026 medium 2026 kotlin rust

Min rows swaps to zero above diagonal

1536. Minimum Swaps to Arrange a Binary Grid medium blog post substack youtube

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Problem TLDR

Min rows swaps to zero above diagonal #medium

Intuition

    // 62% acceptance rate, should be simple
    // 200 nxn=40000
    // count suffix zeros
    // 0
    // 1
    // 2
    // target is
    // n-1
    // n-2
    // ...
    // 1
    // 0
    // or more
    // 012 210
    // how to rearrange optimally?
    // 201
    // 210
    //
    // 022 220
    //
    // 021 210
    //
    // only adjucent means its a bubble sort only
    //

• count suffixes
• bubble rows up

Approach

• we don’t have to add them back

Complexity

• Time complexity: \(O(n^2)\)

• Space complexity: \(O(n)\)

Code

// 22ms
    fun minSwaps(g: Array<IntArray>) =
        ArrayList(g.map { it.lastIndexOf(1) }).run {
            indices.sumOf { i ->
                val j = indices.find { get(it) <= i }
                removeAt(j ?: return -1); j
            }
        }

// 0ms
    pub fn min_swaps(g: Vec<Vec<i32>>) -> i32 {
        let mut s = g.into_iter().map(|r|r.into_iter().rposition(|x|x>0).unwrap_or(0)).collect_vec();
        (0..s.len()).try_fold(0, |r, i| {
            s.iter().position(|&x| x <= i).map(|j|{ s.remove(j); r+j as i32})}).unwrap_or(-1)
    }