[Two Pointers] LC 881. Boats to Save People

  • Given an array people where people[i] is the weight of the ith person, and an infinite number of boats
  • Each boat carries at most two people at the same time
  • Return the minimum number of boats to carry every given person.
  • Set the left = 0, and right = n-1
  • The right pointer is moving at a constant speed: 1 to the left every iteration, given the fact that our worst case scenario is using exactly n boats
  • We are moving the left pointer to break the constant speed → while left < right, and decrease the number of boat used
  • A greedy approach by adding up the largest & smallest element
  • A type of pointer problem with left and right moving toward the opposite direction
  • Strong hint of using greedy
class Solution:
def numRescueBoats(self, people: List[int], limit: int) -> int:

l, r = 0, len(people)-1

while l<=r:
if people[l] + people[r] <=limit:
return res




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