Description Link to heading

881. Boats to Save People (Medium)

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

Solution Link to heading

We should pair the heaviest people with the heaviest peole if the sum of their weight is less than limit, or we just let the heaviest people on one boat.

Code Link to heading 

class Solution {
public:
    int numRescueBoats(vector<int>& people, int limit) {
        std::sort(people.begin(), people.end());
        int left = 0, right = people.size() - 1;
        int cnt = 0;
        while (left <= right) {
            if (people[right] + people[left] <= limit) {
                cnt++;
                right--;
                left++;
            } else {
                cnt++;
                right--;
            }
        }
        return cnt;
    }
};