Boats to Save People

Description

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

Code

Time Complexity: $O(n\log n)$, Space Complexity: $O(1)$

考慮將最重和最輕的人配在一起，如果可以就一起上，不行就重的人自己上。

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

Source

• Boats to Save People - LeetCode