problem0335

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335. Self Crossing

题目

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)

Credits:Special thanks to @dietpepsi for adding this problem and creating all test cases.

解题思路

见程序注释 只会出现下面三种情况