leetcode-go/leetcode/hard/335.self-crossing.go

func isSelfCrossing(x []int) bool {
	// 3 situations for self crossing:
	// 1.     _____    0 intersects 3, x[2] <= x[0] && x[1] <= x[3]
	//       |  1  |
	//      2|     |0
	//       `-----+-
	//          3  |
	//
	// 2.    _____     0 intersects (and coincides) 4,
	//      |  1  |    x[1] == x[3] && x[2] <= x[0] + x[4]
	//     2|     |0
	//      |     |
	//      |_____^4
	//         3
	//
	// 3.    ___       0 intersects 5,
	//      | 1 |  5   x[4] <= x[2] && x[1] <= x[3] && x[2] <= x[0] + x[4] && x[3] <= x[1] + x[5]
	//      | <-+---.
	//     2|   |0  |4
	//      |_______|
	//          3
	//
	n := len(x)
	if n < 4 {
		return false
	}
	for i := 3; i < n; i++ {
		if x[i-1] <= x[i-3] && x[i-2] <= x[i] {
			return true
		}
		if 4 <= i && x[i-3] == x[i-1] && x[i-2] <= x[i-4]+x[i] {
			return true
		}
		if 5 <= i && x[i-1] <= x[i-3] && x[i-4] <= x[i-2] && x[i-3] <= x[i-5]+x[i-1] && x[i-2] <= x[i-4]+x[i] {
			return true
		}
	}
	return false
}