452. Minimum Number of Arrows to Burst Balloons

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Each balloon is a closed interval [start, end] on the x-axis. An arrow shot straight up at position x bursts every balloon with start <= x <= end, and keeps flying, so one arrow can burst many balloons.

Given the balloons in points, return the smallest number of arrows that bursts all of them. Balloons that only touch at an end point, like [1,2] and [2,3], can share one arrow at x = 2.

Example

points = [[10,16],[2,8],[1,6],[7,12]]  ->  2
points = [[1,2],[2,3],[3,4],[4,5]]     ->  2

In the first case, one arrow at x = 6 bursts [2,8] and [1,6], and one at x = 11 bursts [10,16] and [7,12].

Constraints

• 1 <= points.length <= 10^5
• -2^31 <= start <= end <= 2^31 - 1