You are given an array x of n positive numbers. You start at point (0,0) and moves x[0] metres to the north, then x[1] metres to the west, x[2] metres to the south, x[3] metres to the east and so on. In other words, after each move your direction changes counter-clockwise.

Write a one-pass algorithm with O(1) extra space to determine, if your path crosses itself, or not.

Example 1:

Given x =

[2, 1, 1, 2]

,

┌───┐

│   │

└───┼──>

    │

Return true (self crossing)

Example 2:

Given x =

[1, 2, 3, 4]

,

┌──────┐

│      │

│

│

└────────────>

Return false (not self crossing)

Example 3:

Given x =

[1, 1, 1, 1]

,

┌───┐

│   │

└───┼>

Return true (self crossing)

 public class Solution {

     public boolean isSelfCrossing(int[] x) {

         if (x.length <= 3) return false;

         for (int i=3; i<x.length; i++) {

             //check if 4th line cross with the first line and so on

             if (x[i]>=x[i-2] && x[i-1]<=x[i-3]) return true;

             //check if 5th line cross with the first line and so on

             if (i >= 4) {

                 if (x[i-1]==x[i-3] && x[i]+x[i-4]>=x[i-2]) return true;

             }

             //check if 6th line cross with the first line and so on

             if (i >= 5) {

                 if (x[i-2]>=x[i-4] && x[i]>=x[i-2]-x[i-4] && x[i-1]<=x[i-3] && x[i-1]>=x[i-3]-x[i-5]) return true;

             }

         }

         return false;

     }

 }