Minimum Arrows to Burst Balloons

  

Problem

Given a set of balloons (start, end), find number of arrows needed to burst. An arrow bursts all the balloons in its vertical path.



Solution

  • Greedy.
  • Trick is to sort them by 'end'.
  • Keep a current end that for the current row. 
  • Every time, a balloon starts after the current end Increase the arrow count. 
# Greedy

def findMinArrowShots(self, points: List[List[int]]) -> int:
       
        if not points:
            return 0
       
        points.sort(key = lambda x: x[1])   
        cur_end = points[0][1]
        arrow = 1
       
        for start, end in points:
            if start > cur_end:
                arrow += 1
                cur_end = end
        return arrow

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