LeetCode 881 Boats to Save People (两点法)

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

题目链接：https://leetcode.com/problems/boats-to-save-people/

题目大意：n个人，有若干船，每只船最多载两人且总的载重均为limit，问运送这个n个人最少需要多少只船

题目分析：一开始看错题了，以为每只船可以载无限多的人，想了个二分+dp但是题目给的数据范围跑不了，每只最多载两人的话排序扫一下就好了，大的能带小的就带，不能带就自己坐

19ms，时间击败77.42%

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