Self crossing

Array Math Geometry

34.2% acceptance

Jan 12, 2026

416

522

You are given an array of integers distance. You start at the point (0, 0) on an X-Y plane, and you move distance[0] meters to the north, then distance[1] meters to the west, distance[2] meters to the south, distance[3] meters to the east, and so on. In other words, after each move, your direction changes counter-clockwise. Return true if your path crosses itself or false if it does not.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn is_self_crossing(distance: Vec<i32>) -> bool {
    let n = distance.len();
    if n < 4 {
      return false;
    }
    
    for i in 3..n {
      // Fourth line crosses first line
      if distance[i] >= distance[i - 2] && distance[i - 1] <= distance[i - 3] {
        return true;
      }
      
      // Fifth line crosses second line
      if i >= 4 {
        if distance[i - 1] == distance[i - 3]
          && distance[i] + distance[i - 4] >= distance[i - 2] {
          return true;
        }
      }
      
      // Sixth line crosses third line
      if i >= 5 {
        if distance[i - 2] >= distance[i - 4]
          && distance[i] + distance[i - 4] >= distance[i - 2]
          && distance[i - 1] + distance[i - 5] >= distance[i - 3]
          && distance[i - 1] <= distance[i - 3] {
          return true;
        }
      }
    }
    
    false
  }
}