1
class Solution {
2

3
  public boolean isSelfCrossing(int[] x) {
4
    boolean arm = false;
5
    boolean leg = false;
6
    for (int i = 2; i < x.length; ++i) {
7
      int a = f(x, i - 2) - f(x, i - 4);
8
      int b = f(x, i - 2);
9

10
      if (arm && x[i] >= b) return true; // cross [i - 2]
11
      if (leg && x[i] >= a && a > 0) return true; // cross [i - 4]
12

13
      if (x[i] < a) arm = true;
14
      else if (x[i] <= b) leg = true;
15
    }
16
    return false;
17
  }
18

19
  private int f(int[] x, int index) {
20
    return (index < 0) ? 0 : x[index];
21
  }
22
}