LeetCode Boats to Save People Solution
You are given an array people
where people[i]
is the weight of the ith
person, and an infinite number of boats where each boat can carry a maximum weight of limit
. Each boat carries at most two people at the same time, provided the sum of the weight of those people is at most limit
.
Return the minimum number of boats to carry every given person.
Example 1:
Input: people = [1,2], limit = 3
Output: 1
Explanation: 1 boat (1, 2)
Example 2:
Input: people = [3,2,2,1], limit = 3
Output: 3
Explanation: 3 boats (1, 2), (2) and (3)
Example 3:
Input: people = [3,5,3,4], limit = 5
Output: 4
Explanation: 4 boats (3), (3), (4), (5)
Constraints:
1 <= people.length <= 5 * 104
1 <= people[i] <= limit <= 3 * 104
Problem Link: https://leetcode.com/problems/boats-to-save-people/
Solution
We wish to perform two pointers in opposite directions on a sorted array people
.
To optimize the number of boats, we can assign a light weight person with a heavy person.
Just as Two Sum Sorted try to pair two numbers adding up to sum
, we try to pair two people with weight less than or equal to limit
.
If their total weight is more than the limit, then we can only assign the person with the heavier weight (person[r]
) onto the boat so that the lighter person may be paired with someone else.
Implementation
1def numRescueBoats(self, people: List[int], limit: int) -> int:
2 people.sort()
3 l, r = 0 , len(people)-1
4 boat = 0
5 while l <= r:
6 if people[l] + people[r] <= limit:
7 l += 1
8 boat += 1
9 r -= 1
10 return boat