# Boats to Save People

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
```

分析

因为船只能载2人每次，所以可以双指针夹逼，注意是 l<=r

```
class Solution:
    def numRescueBoats(self, people: List[int], limit: int) -> int:                
        temp = res = 0 
        l = 0
        r = len(people)-1
        people.sort()

        while l <= r:
            if people[l] +people[r] <= limit:
                res += 1
                l += 1
                r-=1
            else:
                res+=1
                r-=1
        return res
```


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