leetcode 735[medium]---Asteroid Collision

难度：medium

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We are given an array asteroids of integers representing asteroids in a row.

For each asteroid, the absolute value represents its size, and the sign represents its direction (positive meaning right, negative meaning left). Each asteroid moves at the same speed.

Find out the state of the asteroids after all collisions. If two asteroids meet, the smaller one will explode. If both are the same size, both will explode. Two asteroids moving in the same direction will never meet.

Example 1:

Input: asteroids = [5, 10, -5]Output: [5, 10]Explanation: The 10 and -5 collide resulting in 10.  The 5 and 10 never collide.

Example 2:

Input: asteroids = [8, -8]Output: []Explanation: The 8 and -8 collide exploding each other.

Example 3:

Input: asteroids = [10, 2, -5]Output: [10]Explanation: The 2 and -5 collide resulting in -5.  The 10 and -5 collide resulting in 10.

Example 4:

Input: asteroids = [-2, -1, 1, 2]Output: [-2, -1, 1, 2]Explanation: The -2 and -1 are moving left, while the 1 and 2 are moving right.Asteroids moving the same direction never meet, so no asteroids will meet each other.

Note:

The length of asteroids will be at most 10000.

Each asteroid will be a non-zero integer in the range [-1000, 1000]..

思路：给定一个array，如果正数在前，负数在后，两者相碰取绝对值较大者，消掉另一个数。保留下来的数如果是负数，可以继续与其前面的正数相消。 如果两者绝对值相同，两个数都被消掉。如果负数在前，正数在后，消除反应不会进行。

          借鉴别人的code，While循环找到每次调整以后的之后是负数的正数的索引。

          for 循环比较正数与负数，用pop()删除消除的数。shrink 用来调整消除后i的位置。

          膜拜这种简直是在用python写故事的大神。