0452. Minimum Number of Arrows to Burst Balloons
https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons
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
ac
class Solution {
public int findMinArrowShots(int[][] points) {
if (points.length == 0) return 0;
Arrays.sort(points, (a, b) -> {return a[1] - b[1];});
int shotPoint = points[0][1], cnt = 1;
for (int[] p : points) {
// System.out.println(String.format("p[0]:%s, p[1]:%s, shotPoint:%s", p[0], p[1], shotPoint));
if (p[0] > shotPoint) {
cnt++;
shotPoint = p[1];
}
}
return cnt;
}
}
/*
1) sort by end point asc; 2) maintain shotPoint, when next interval start point > shotPoint, update shotPoint to its end, cnt++;
*/
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