469. Convex Polygon

Given a list of points that form a polygon when joined sequentially, find if this polygon is convex (Convex polygon definition) .

Note:

1. There are at least 3 and at most 10,000 points.
2. Coordinates are in the range -10,000 to 10,000.
3. You may assume the polygon formed by given points is always a simple polygon (Simple polygon definition) . In other words, we ensure that exactly two edges intersect at each vertex, and that edges otherwise don't intersect each other .

Example 1:

[[0,0],[0,1],[1,1],[1,0]]
Answer: True
Explanation:

Example 2:

[[0,0],[0,10],[10,10],[10,0],[5,5]]
Answer: False
Explanation:

1、题目描述¶

给定一个按顺序连接的多边形的顶点，判断该多边形是否为凸多边形。（凸多边形的定义）

注：

1. 顶点个数至少为 3 个且不超过 10,000。
2. 坐标范围为 -10,000 到 10,000。
3. 你可以假定给定的点形成的多边形均为简单多边形（简单多边形的定义）。换句话说，保证每个顶点处恰好是两条边的汇合点，并且这些边 互不相交 。

示例 1：

[[0,0],[0,1],[1,1],[1,0]]

输出： True

解释：

示例 2：

[[0,0],[0,10],[10,10],[10,0],[5,5]]

输出： False

解释：