0881. Boats to Save People (M)

Boats to Save People (M)

题目

The i-th person has weight people[i], and each boat can carry a maximum weight of limit.

Each boat carries at most 2 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. (It is guaranteed each person can be carried by a boat.)

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)

Note:

• 1 <= people.length <= 50000
• 1 <= people[i] <= limit <= 30000

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题目

规定一艘船最多可以载两人，且有限定载重量。给定n个人的重量，判断最少需要几艘船能运送所有人。

思路

贪心 + Two Pointers。先对数组排序，每次一定会安排一个最重的一人上船，这时判断还未上船的最轻的人能否也挤上去。重复直到所有人都上船。

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代码实现

Java

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