added problem73

Author: dampdigits

problem73/README.md

@@ -0,0 +1,37 @@
+# 452. Minimum Number of Arrows to Burst Balloons
+
+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