LeetCode 881. 救生艇（贪心，双指针）

示例 1：
输入：people = [1,2], limit = 3
输出：1
解释：1 艘船载 (1, 2)

示例 2：
输入：people = [3,2,2,1], limit = 3
输出：3
解释：3 艘船分别载 (1, 2), (2) 和 (3)

示例 3：
输入：people = [3,5,3,4], limit = 5
输出：4
解释：4 艘船分别载 (3), (3), (4), (5)

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

class Solution {
public:
    int numRescueBoats(vector<int>& people, int limit) {
        sort(people.begin(), people.end());
        int i = 0, j = people.size()-1, count = 0, w = 0, p = 0;
        while(i <= j)
        {
        	while(j >= 0 && p < 2 && w+people[j] <= limit)
        	{
        		w += people[j];
        		++p;//一条船最多两人
        		--j;
        	}
        	while(i <= j && p < 2 && w+people[i] <= limit)
        	{
        		w += people[i];
        		++p;
        		++i;
        	}
        	count++;
        	p = 0;
        	w = 0;
        }
        return count;
    }
};