[Swift]LeetCode881. 救生艇 | Boats to Save People

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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

---

第 i 我的的体重为 people[i]，每艘船能够承载的最大重量为 limit。

每艘船最多可同时载两人，但条件是这些人的重量之和最多为 limit。

返回载到每个人所需的最小船数。(保证每一个人都能被船载)。

 

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

---

664ms

 

 1 class Solution {
 2     func numRescueBoats(_ people: [Int], _ limit: Int) -> Int {
 3         let people = people.sorted()
 4         var left = 0, right = people.count - 1
 5         var count = 0
 6         while left <= right {
 7             if people[left] + people[right] <= limit {
 8                 count += 1
 9                 left += 1
10                 right -= 1
11             } else {
12                 count += 1
13                 right -= 1
14             }
15         }
16         return count        
17     }
18 }

---

Runtime: 708 ms

Memory Usage: 19.8 MB

 1 class Solution {
 2     func numRescueBoats(_ people: [Int], _ limit: Int) -> Int {
 3         var people = people.sorted(by:<)
 4         var ans:Int = 0
 5         var hi:Int = people.count - 1
 6         var lo:Int = 0 
 7         while (hi >= lo)
 8         {
 9             if people[lo] + people[hi] <= limit
10             {
11                 lo += 1
12             }
13             hi -= 1
14             ans += 1
15         }
16         return ans
17     }
18 }

---

764ms

 1 class Solution {
 2     func numRescueBoats(_ people: [Int], _ limit: Int) -> Int {
 3         var people = people.sorted()
 4         var ans = 0, headIndex = 0, tailIndex = people.count - 1
 5         while headIndex <= tailIndex {
 6             ans += 1
 7             var lastTailIndex = tailIndex
 8             while tailIndex > headIndex {
 9                 if people[tailIndex]+people[headIndex] > limit {
10                     tailIndex -= 1
11                     if tailIndex == headIndex {
12                         ans += (lastTailIndex - headIndex)
13                         return ans
14                     }
15                 }else {
16                     ans += (lastTailIndex - tailIndex)
17                     tailIndex -= 1
18                     break
19                 }
20             }
21             headIndex += 1
22         }
23         return ans
24     }
25 }