# Popping Balloons

greedy**Balloons on a Board**

There are some spherical balloons taped onto a flat wall that represents the XY-plane. The balloons are represented as a 2D integer array points where points[i] = [x_start, x_end] denotes a balloon whose horizontal diameter stretches between xstart and xend. You do not know the exact y-coordinates of the balloons.

Arrows can be shot up directly vertically (in the positive y-direction) from different points along the x-axis. A balloon with x_start and x_end is burst by an arrow shot at x if x_start ≤ x ≤ x_end. There is no limit to the number of arrows that can be shot. A shot arrow keeps traveling up infinitely, bursting any balloons in its path.

Given the array points, return the minimum number of arrows that must be shot to burst all balloons.

## Example

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0 5 10 15 20

Output: 2

Explanation: The balloons can be burst by 2 arrows:

- Shoot an arrow at x = 6, bursting the balloons [2,8] and [1,6].

- Shoot an arrow at x = 11, bursting the balloons [10,16] and [7,12].