feat: add solutions to lc problem: No.0881

yanglbme · yanglbme · commit ec01a109ed60 · 2022-10-16T20:16:28.000+08:00
No.0881.Boats to Save People
diff --git a/solution/0800-0899/0881.Boats to Save People/README.md b/solution/0800-0899/0881.Boats to Save People/README.md
@@ -50,7 +50,11 @@
 
 <!-- 这里可写通用的实现逻辑 -->
 
-“排序 + 双指针”实现。
+**方法一：贪心 + 双指针**
+
+排序后，使用双指针分别指向数组首尾，每次取两个指针指向的元素之和与 `limit` 比较，如果小于等于 `limit`，则两个指针同时向中间移动一位，否则只移动右指针。累加答案即可。
+
+时间复杂度 $O(n\log n)$，其中 $n$ 为数组 `people` 的长度。
 
 <!-- tabs:start -->
 
@@ -62,13 +66,14 @@
 class Solution:
     def numRescueBoats(self, people: List[int], limit: int) -> int:
         people.sort()
-        num, i, j = 0, 0, len(people) - 1
+        ans = 0
+        i, j = 0, len(people) - 1
         while i <= j:
             if people[i] + people[j] <= limit:
                 i += 1
             j -= 1
-            num += 1
-        return num
+            ans += 1
+        return ans
 ```
 
 ### **Java**
@@ -79,17 +84,50 @@ class Solution:
 class Solution {
     public int numRescueBoats(int[] people, int limit) {
         Arrays.sort(people);
-        int num = 0;
-        int i = 0, j = people.length - 1;
-        while (i <= j) {
+        int ans = 0;
+        for (int i = 0, j = people.length - 1; i <= j; --j) {
+            if (people[i] + people[j] <= limit) {
+                ++i;
+            }
+            ++ans;
+        }
+        return ans;
+    }
+}
+```
+
+### **C++**
+
+```cpp
+class Solution {
+public:
+    int numRescueBoats(vector<int>& people, int limit) {
+        sort(people.begin(), people.end());
+        int ans = 0;
+        for (int i = 0, j = people.size() - 1; i <= j; --j) {
             if (people[i] + people[j] <= limit) {
                 ++i;
             }
-            --j;
-            ++num;
+            ++ans;
         }
-        return num;
+        return ans;
     }
+};
+```
+
+### **Go**
+
+```go
+func numRescueBoats(people []int, limit int) int {
+	sort.Ints(people)
+	ans := 0
+	for i, j := 0, len(people)-1; i <= j; j-- {
+		if people[i]+people[j] <= limit {
+			i++
+		}
+		ans++
+	}
+	return ans
 }
 ```
 
diff --git a/solution/0800-0899/0881.Boats to Save People/README_EN.md b/solution/0800-0899/0881.Boats to Save People/README_EN.md
@@ -51,13 +51,14 @@
 class Solution:
     def numRescueBoats(self, people: List[int], limit: int) -> int:
         people.sort()
-        num, i, j = 0, 0, len(people) - 1
+        ans = 0
+        i, j = 0, len(people) - 1
         while i <= j:
             if people[i] + people[j] <= limit:
                 i += 1
             j -= 1
-            num += 1
-        return num
+            ans += 1
+        return ans
 ```
 
 ### **Java**
@@ -66,20 +67,53 @@ class Solution:
 class Solution {
     public int numRescueBoats(int[] people, int limit) {
         Arrays.sort(people);
-        int num = 0;
-        int i = 0, j = people.length - 1;
-        while (i <= j) {
+        int ans = 0;
+        for (int i = 0, j = people.length - 1; i <= j; --j) {
             if (people[i] + people[j] <= limit) {
                 ++i;
             }
-            --j;
-            ++num;
+            ++ans;
         }
-        return num;
+        return ans;
     }
 }
 ```
 
+### **C++**
+
+```cpp
+class Solution {
+public:
+    int numRescueBoats(vector<int>& people, int limit) {
+        sort(people.begin(), people.end());
+        int ans = 0;
+        for (int i = 0, j = people.size() - 1; i <= j; --j) {
+            if (people[i] + people[j] <= limit) {
+                ++i;
+            }
+            ++ans;
+        }
+        return ans;
+    }
+};
+```
+
+### **Go**
+
+```go
+func numRescueBoats(people []int, limit int) int {
+	sort.Ints(people)
+	ans := 0
+	for i, j := 0, len(people)-1; i <= j; j-- {
+		if people[i]+people[j] <= limit {
+			i++
+		}
+		ans++
+	}
+	return ans
+}
+```
+
 ### **...**
 
 ```
diff --git a/solution/0800-0899/0881.Boats to Save People/Solution.cpp b/solution/0800-0899/0881.Boats to Save People/Solution.cpp
@@ -0,0 +1,14 @@
+class Solution {
+public:
+    int numRescueBoats(vector<int>& people, int limit) {
+        sort(people.begin(), people.end());
+        int ans = 0;
+        for (int i = 0, j = people.size() - 1; i <= j; --j) {
+            if (people[i] + people[j] <= limit) {
+                ++i;
+            }
+            ++ans;
+        }
+        return ans;
+    }
+};
diff --git a/solution/0800-0899/0881.Boats to Save People/Solution.go b/solution/0800-0899/0881.Boats to Save People/Solution.go
@@ -0,0 +1,11 @@
+func numRescueBoats(people []int, limit int) int {
+	sort.Ints(people)
+	ans := 0
+	for i, j := 0, len(people)-1; i <= j; j-- {
+		if people[i]+people[j] <= limit {
+			i++
+		}
+		ans++
+	}
+	return ans
+}
diff --git a/solution/0800-0899/0881.Boats to Save People/Solution.java b/solution/0800-0899/0881.Boats to Save People/Solution.java
@@ -1,15 +1,13 @@
 class Solution {
     public int numRescueBoats(int[] people, int limit) {
         Arrays.sort(people);
-        int num = 0;
-        int i = 0, j = people.length - 1;
-        while (i <= j) {
+        int ans = 0;
+        for (int i = 0, j = people.length - 1; i <= j; --j) {
             if (people[i] + people[j] <= limit) {
                 ++i;
             }
-            --j;
-            ++num;
+            ++ans;
         }
-        return num;
+        return ans;
     }
 }
diff --git a/solution/0800-0899/0881.Boats to Save People/Solution.py b/solution/0800-0899/0881.Boats to Save People/Solution.py
@@ -1,10 +1,11 @@
 class Solution:
     def numRescueBoats(self, people: List[int], limit: int) -> int:
         people.sort()
-        num, i, j = 0, 0, len(people) - 1
+        ans = 0
+        i, j = 0, len(people) - 1
         while i <= j:
             if people[i] + people[j] <= limit:
                 i += 1
             j -= 1
-            num += 1
-        return num
+            ans += 1
+        return ans
diff --git a/solution/2400-2499/2441.Largest Positive Integer That Exists With Its Negative/README.md b/solution/2400-2499/2441.Largest Positive Integer That Exists With Its Negative/README.md
@@ -50,7 +50,11 @@
 
 <!-- 这里可写通用的实现逻辑 -->
 
-**方法一：枚举**
+**方法一：哈希表 + 枚举**
+
+我们先用哈希表 $s$ 记录数组中的所有元素，然后枚举数组中的每个元素 $x$，如果 $x$ 为正数，且 $-x$ 在哈希表 $s$ 中，更新答案。
+
+时间复杂度 $O(n)$，空间复杂度 $O(n)$。其中 $n$ 为数组的长度。
 
 <!-- tabs:start -->
 
diff --git a/solution/CONTEST_README.md b/solution/CONTEST_README.md
@@ -11,8 +11,8 @@
 
 | 段位  | 比例   | 段位名   | 国服分数线    | 勋章                                                                    |
 | ----- | ------ | -------- | --------- | --------------------------------------------------------------------------- |
-| LV3 | 5%  | Guardian | &ge;2221.96 | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Guardian.gif" style="width: 80px;" /></p> |
-| LV2 | 20% | Knight   | &ge;1869.96 | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Knight.gif" style="width: 80px;" /></p>   |
+| LV3 | 5%  | Guardian | &ge;2225.82 | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Guardian.gif" style="width: 80px;" /></p> |
+| LV2 | 20% | Knight   | &ge;1871.95 | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Knight.gif" style="width: 80px;" /></p>   |
 | LV1 | 75% | -        | -         | -                                                                           |
 
 力扣竞赛 **全国排名前 10** 的用户，全站用户名展示为品牌橙色。
diff --git a/solution/CONTEST_README_EN.md b/solution/CONTEST_README_EN.md
@@ -13,8 +13,8 @@ If you are in the top 25% of the contest rating, you’ll get the “Knight” b
 
 | Level | Proportion | Badge      | Rating |                                                                                                                         |
 | ----- | ---------- | ---------- | -------------- | ----------------------------------------------------------------------------------------------------------------------- |
-| LV3 | 5\%      | Guardian | &ge;2175.86   | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Guardian.gif" style="width: 80px;" /></p> |
-| LV2 | 20\%     | Knight   | &ge;1850.05   | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Knight.gif" style="width: 80px;" /></p>   |
+| LV3 | 5\%      | Guardian | &ge;2178.58   | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Guardian.gif" style="width: 80px;" /></p> |
+| LV2 | 20\%     | Knight   | &ge;1851.23   | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Knight.gif" style="width: 80px;" /></p>   |
 | LV1 | 75\%     | -          | -              | -                                                                                                                       |
 
 For top 10 users (excluding LCCN users), your LeetCode ID will be colored orange on the ranking board. You'll also have the honor with you when you post/comment under discuss.
diff --git a/solution/contest.py b/solution/contest.py
@@ -127,8 +127,8 @@ def generate_contest_list():
 
 | 段位  | 比例   | 段位名   | 国服分数线    | 勋章                                                                    |
 | ----- | ------ | -------- | --------- | --------------------------------------------------------------------------- |
-| LV3 | 5%  | Guardian | &ge;2221.96 | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Guardian.gif" style="width: 80px;" /></p> |
-| LV2 | 20% | Knight   | &ge;1869.96 | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Knight.gif" style="width: 80px;" /></p>   |
+| LV3 | 5%  | Guardian | &ge;2225.82 | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Guardian.gif" style="width: 80px;" /></p> |
+| LV2 | 20% | Knight   | &ge;1871.95 | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Knight.gif" style="width: 80px;" /></p>   |
 | LV1 | 75% | -        | -         | -                                                                           |
 
 力扣竞赛 **全国排名前 10** 的用户，全站用户名展示为品牌橙色。
@@ -153,8 +153,8 @@ def generate_contest_list():
 
 | Level | Proportion | Badge      | Rating |                                                                                                                         |
 | ----- | ---------- | ---------- | -------------- | ----------------------------------------------------------------------------------------------------------------------- |
-| LV3 | 5\%      | Guardian | &ge;2175.86   | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Guardian.gif" style="width: 80px;" /></p> |
-| LV2 | 20\%     | Knight   | &ge;1850.05   | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Knight.gif" style="width: 80px;" /></p>   |
+| LV3 | 5\%      | Guardian | &ge;2178.58   | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Guardian.gif" style="width: 80px;" /></p> |
+| LV2 | 20\%     | Knight   | &ge;1851.23   | <p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/images/Knight.gif" style="width: 80px;" /></p>   |
 | LV1 | 75\%     | -          | -              | -                                                                                                                       |
 
 For top 10 users (excluding LCCN users), your LeetCode ID will be colored orange on the ranking board. You'll also have the honor with you when you post/comment under discuss.

Original file line number	Diff line number	Diff line change
`@@ -1,15 +1,13 @@`
`1`	`1`	`class Solution {`
`2`	`2`	`public int numRescueBoats(int[] people, int limit) {`
`3`	`3`	`Arrays.sort(people);`
`4`		`- int num = 0;`
`5`		`- int i = 0, j = people.length - 1;`
`6`		`- while (i <= j) {`
	`4`	`+ int ans = 0;`
	`5`	`+ for (int i = 0, j = people.length - 1; i <= j; --j) {`
`7`	`6`	`if (people[i] + people[j] <= limit) {`
`8`	`7`	`++i;`
`9`	`8`	`}`
`10`		`- --j;`
`11`		`- ++num;`
	`9`	`+ ++ans;`
`12`	`10`	`}`
`13`		`- return num;`
	`11`	`+ return ans;`
`14`	`12`	`}`
`15`	`13`	`}`