LeetCode 881. Boats to Save People解题（Python）
题目如下：
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 <= 500001 <= people[i] <= limit <= 30000
解题：
这是经典的贪心问题，下面是O(n)复杂度的解决方案：
class Solution(object):
def numRescueBoats(self, people, limit):
"""
:type people: List[int]
:type limit: int
:rtype: int
"""
people.sort()
result = 0
i = 0
j = len(people) - 1
while j >= i:
if people[i] + people[j] <= limit:
i += 1
j -= 1
result += 1
return result
