881. Boats to Save People

1. Questions

You are given an array people where people[i] is the weight of the i^th 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.

2. Examples

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)

3. Constraints

• 1 <= people.length <= 5 * 10⁴
• 1 <= people[i] <= limit <= 3 * 10⁴

4. References

来源：力扣（LeetCode） 链接：https://leetcode-cn.com/problems/boats-to-save-people 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

5. Solutions

class Solution {
    public int numRescueBoats(int[] people, int limit) {
        int res = 0;
        int head = 0;
        int tail = people.length - 1;
        Arrays.sort(people);
        while (head <= tail) {
            if (people[head] + people[tail] <= limit) {
                head++;
            }
            tail--;
            res++;
        }
        return res;
    }
}