LeetCode Entry

2069. Walking Robot Simulation II

07.04.2026 medium 2026 kotlin rust

Implement perimeter-robot

2069. Walking Robot Simulation II medium substack youtube

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Problem TLDR

Implement perimeter-robot #medium

Intuition

// 15 minute: so this TLE
//
// does robot always goes on perimeter? -- yes
//
// make it linear
//
// xxxxxyyyxxxxxyyyxxxxxyyyxxxxxyyy
//  w    h   w   h 0
//
// each rotation is extra step? - no

1. its only the perimeter
2. w-1, h-1
3. top-down south

Approach

• extract separate method

Complexity

• Time complexity: \(O(n)\)

• Space complexity: \(O(1)\)

Code

// 146ms
class Robot(a: Int, b: Int, var p: Int = 0) {
    val w=a-1; val h=b-1; val wh=w+w+h+h
    val i get() = when (val m = p % wh) {
        in 0..w -> listOf(m, 0) to if(m==0 && p>0) "South" else "East"
        in 0..w+h -> listOf(w, m-w) to "North"
        in 0..wh-h -> listOf(wh-h-m, h) to "West"
        else -> listOf(0, wh-m) to "South"
    }
    fun step(n: Int) { p += n }; fun getPos() = i.first; fun getDir() = i.second
}

// 16ms
struct Robot(i32, i32, i32, i32); impl Robot {
    fn new(a: i32, b: i32) -> Self { Self(a-1, b-1, 2*a+2*b-4, 0) }
    fn step(&mut self, n: i32) { self.3 += n }
    fn i(&self) -> (Vec<i32>, &'static str) {
        let (w, h, t, p, m) = (self.0, self.1, self.2, self.3, self.3 % self.2);
        if m <= w { (vec![m, 0], if p>0 && m==0 {"South"} else {"East"}) }
        else if m <= w+h { (vec![w, m-w], "North") }
        else if m <= t-h { (vec![t-h-m, h], "West") }
        else { (vec![0, t-m], "South") }
    }
    fn get_pos(&self) -> Vec<i32> { self.i().0 }
    fn get_dir(&self) -> String { self.i().1.into() }
}