Minimum Number of Arrows to Burst Balloons - LeetCode

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] = [xstart, xend] 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 xstart and xend is burst by an arrow shot at x if xstart <= x <= xend. 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 1: Input: points = [[10,16],[2,8],[1,6],[7,12]] 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].

Example 2: Input: points = [[1,2],[3,4],[5,6],[7,8]] Output: 4 Explanation: One arrow needs to be shot for each balloon for a total of 4 arrows.

Example 3: Input: points = [[1,2],[2,3],[3,4],[4,5]] Output: 2 Explanation: The balloons can be burst by 2 arrows: - Shoot an arrow at x = 2, bursting the balloons [1,2] and [2,3]. - Shoot an arrow at x = 4, bursting the balloons [3,4] and [4,5].

Constraints:

```
1 <= points.length <= 105
points[i].length == 2
-231 <= xstart < xend <= 231 - 1
```

- code

```
class Solution:
def findMinArrowShots(self, points: List[List[int]]) -> int:
points.sort()
last_e = points[0][1]
arrows = 1
for cur_s, cur_e in points:
if cur_s <= last_e:
if cur_e >= last_e: continue
elif cur_e < last_e: last_e = cur_e
else:
arrows += 1
last_e = cur_e
return arrows
```

- code

```
class Solution {
public int findMinArrowShots(int[][] points) {
Arrays.sort(points, (a, b) -> {
if (a[1] == b[1]) return 0;
if (a[1] < b[1]) return -1;
return 1;
});
int arrows = 1;
int lastEnd = points[0][1];
int curStart, curEnd;
for (int[] p: points){
curStart = p[0];
curEnd = p[1];
if (curStart > lastEnd){
arrows++;
lastEnd = curEnd;
}
}
return arrows;
}
}
```