881.Boats to Save People

Tags: Medium Greedy

Links: https://leetcode.com/problems/boats-to-save-people/submissions/

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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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class Solution {
public:
    int numRescueBoats(vector<int>& people, int limit) {
        std::ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout.tie(NULL);

        int n = people.size();
        int cnt = 0;

        sort(people.begin(), people.end());
        int start = 0, end = n - 1;
        while (start <= end) {
            if (people[start] + people[end] > limit) {
                ++cnt; --end;
            }
            else {
                ++cnt; ++start; --end;
            }
        }

        return cnt;
    }
};

很典型的贪心问题之乘船问题，胖的和瘦的乘坐一条船。