**Problem Description:**

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

**Solution:**

Algorithm:

- Sort the intervals based on the second values of the given intervals.
- Initialise a count and a possibleEnd. Here possibleEnd can be of type long initialised with the minimum value.
- for int [] p: points -> Check whether the start, that is, p[0] > possibleEnd. If true then -> Update the end with p[1] and increment the count
- Finally return this count to get the number of arrows required.

**Code:**

```
class Solution {
public int findMinArrowShots(int[][] points) {
if (points.length == 0)
return 0;
Arrays.sort(points, (a, b) -> Integer.compare(a[1], b[1]));
int arrowCount = 0;
long possibleEnd = Long.MIN_VALUE;
for (int [] p: points) {
if (p[0] > possibleEnd) {
possibleEnd = p[1];
arrowCount += 1;
}
}
return arrowCount;
}
}
```

## Top comments (0)