leetcode SelfCrossing
z
 2019-04-09 10:36:27   
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public class SelfCrossing {
  /**
   * 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.
   */
  public boolean isSelfCrossing(int[] x) {
    int n = x.length;
    if (n < 4)
      return false;
    for (int i=3; i<n; i++){
      if (i==4){
        if ((x[0] < x[2]) || ((x[0] > x[2]) && (x[1] > x[3])))
          return true;
      }
    }
    return false;
  }
}