Self Crossing

Total Accepted: 1571 Total Submissions: 9025 Difficulty: Medium
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)

思路

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