Merge pull request #421 from LetMeFly666/881

添加问题“881.救生艇”的代码和题解

Author: LetMeFly666

CHANGELOG.md

@@ -0,0 +1,23 @@
+/*
+ * @Author: LetMeFly
+ * @Date: 2024-06-10 15:16:16
+ * @LastEditors: LetMeFly
+ * @LastEditTime: 2024-06-10 15:17:50
+ */
+#ifdef _WIN32
+#include "_[1,2]toVector.h"
+#endif
+
+class Solution {
+public:
+    int numRescueBoats(vector<int>& people, int limit) {
+        sort(people.begin(), people.end());
+        int ans = 0;
+        for (int l = 0, r = people.size() - 1; l <= r; ans++, r--) {
+            if (people[l] + people[r] <= limit) {
+                l++;
+            }
+        }
+        return ans;
+    }
+};

Codes/0881-boats-to-save-people_20240610-sampleVersion.cpp

@@ -0,0 +1,27 @@
+/*
+ * @Author: LetMeFly
+ * @Date: 2024-06-10 15:13:13
+ * @LastEditors: LetMeFly
+ * @LastEditTime: 2024-06-10 15:15:40
+ */
+#ifdef _WIN32
+#include "_[1,2]toVector.h"
+#endif
+
+class Solution {
+public:
+    int numRescueBoats(vector<int>& people, int limit) {
+        sort(people.begin(), people.end());
+        int ans = 0;
+        for (int l = 0, r = people.size() - 1; l <= r;) {
+            if (people[l] + people[r] <= limit) {  // 不用特判l是否等于r
+                l++, r--;
+            }
+            else {
+                r--;
+            }
+            ans++;
+        }
+        return ans;
+    }
+};

Codes/0881-boats-to-save-people_20240610.cpp

@@ -0,0 +1,20 @@
+/*
+ * @Author: LetMeFly
+ * @Date: 2024-06-10 15:25:02
+ * @LastEditors: LetMeFly
+ * @LastEditTime: 2024-06-10 15:27:28
+ */
+package main
+
+import "sort"
+
+func numRescueBoats(people []int, limit int) int {
+    sort.Ints(people);
+    ans := 0
+    for l, r := 0, len(people) - 1; l <= r; ans, r = ans + 1, r - 1 {
+        if people[l] + people[r] <= limit {
+            l++;
+        }
+    }
+    return ans
+}

Codes/0881-boats-to-save-people_20240610.go

@@ -0,0 +1,20 @@
+/*
+ * @Author: LetMeFly
+ * @Date: 2024-06-10 15:21:02
+ * @LastEditors: LetMeFly
+ * @LastEditTime: 2024-06-10 15:23:36
+ */
+import java.util.Arrays;
+
+class Solution {
+    public int numRescueBoats(int[] people, int limit) {
+        Arrays.sort(people);
+        int ans = 0;
+        for (int l = 0, r = people.length - 1; l <= r; ans++, r--) {
+            if (people[l] + people[r] <= limit) {
+                l++;
+            }
+        }
+        return ans;
+    }
+}

Codes/0881-boats-to-save-people_20240610.java

@@ -0,0 +1,19 @@
+'''
+Author: LetMeFly
+Date: 2024-06-10 15:18:38
+LastEditors: LetMeFly
+LastEditTime: 2024-06-10 15:19:51
+'''
+from typing import List
+
+class Solution:
+    def numRescueBoats(self, people: List[int], limit: int) -> int:
+        people.sort()
+        ans = 0
+        l, r = 0, len(people) - 1
+        while l <= r:
+            if people[l] + people[r] <= limit:
+                l += 1
+            r -= 1
+            ans += 1
+        return ans

Codes/0881-boats-to-save-people_20240610.py

@@ -0,0 +1,64 @@
+/*
+ * @Author: LetMeFly
+ * @Date: 2024-06-08 12:06:19
+ * @LastEditors: LetMeFly
+ * @LastEditTime: 2024-06-08 13:42:22
+ */
+#ifdef _WIN32
+#include "_[1,2]toVector.h"
+#endif
+
+class Solution {
+private:
+    int** visited;
+    int size;
+    reference_wrapper<std::vector<int>> a;
+
+    int dfs(int l, int r, int val) {  // [l, r)
+        if (l + 1 >= r) {
+            return 0;
+        }
+        if (visited[l][r - 1]) {
+            return visited[l][r - 1];
+        }
+        int ans = 0;
+        if (a.get()[l] + a.get()[l + 1] == val) {
+            ans = max(ans, 1 + dfs(l + 2, r, val));
+        }
+        if (a.get()[r - 1] + a.get()[r - 2] == val) {
+            ans = max(ans, 1 + dfs(l, r - 2, val));
+        }
+        if (a.get()[l] + a.get()[r - 1] == val) {
+            ans = max(ans, 1 + dfs(l + 1, r - 1, val));
+        }
+        return visited[l][r - 1] = ans;
+    }
+
+    int get(int val) {
+        // memset(visited, 0, sizeof(visited));  // 报错
+        // memset(visited, 0, sizeof(int) * size * size);  // 报错
+        for (int i = 0; i < size; i++) {
+            memset(visited[i], 0, size * sizeof(int));
+        }
+        return dfs(0, size, val);
+    }
+public:
+    Solution() : a(*(new std::vector<int>)) {}
+
+    ~Solution() {
+        for (int i = 0; i < size; i++) {
+            delete[] visited[i];
+        }
+        delete[] visited;
+    }
+
+    int maxOperations(vector<int>& nums) {
+        a = nums;
+        size = nums.size();
+        visited = new int*[size];
+        for (int i = 0; i < size; i++) {
+            visited[i] = new int[size];
+        }
+        return max(get(nums[0] + nums[1]), max(get(nums[size - 1] + nums[size - 2]), get(nums[0] + nums[size - 1])));
+    }
+};

Codes/3040-maximum-number-of-operations-with-the-same-score-ii.cpp

@@ -272,6 +272,7 @@
 |0873.最长的斐波那契子序列的长度|中等|<a href="https://leetcode.cn/problems/length-of-longest-fibonacci-subsequence/" target="_blank">题目地址</a>|<a href="https://blog.letmefly.xyz/2022/07/09/LeetCode%200873.%E6%9C%80%E9%95%BF%E7%9A%84%E6%96%90%E6%B3%A2%E9%82%A3%E5%A5%91%E5%AD%90%E5%BA%8F%E5%88%97%E7%9A%84%E9%95%BF%E5%BA%A6/" target="_blank">题解地址</a>|<a href="https://letmefly.blog.csdn.net/article/details/125690924" target="_blank">CSDN题解</a>|<a href="https://leetcode.cn/problems/length-of-longest-fibonacci-subsequence/solution/by-tisfy-4gh4/" target="_blank">LeetCode题解</a>|
 |0874.模拟行走机器人|中等|<a href="https://leetcode.cn/problems/walking-robot-simulation/solutions/" target="_blank">题目地址</a>|<a href="https://blog.letmefly.xyz/2023/07/19/LeetCode%200874.%E6%A8%A1%E6%8B%9F%E8%A1%8C%E8%B5%B0%E6%9C%BA%E5%99%A8%E4%BA%BA/" target="_blank">题解地址</a>|<a href="https://letmefly.blog.csdn.net/article/details/131800691" target="_blank">CSDN题解</a>|<a href="https://leetcode.cn/problems/walking-robot-simulation/solutions/2349728/letmefly-874mo-ni-xing-zou-ji-qi-ren-ha-90cbo/" target="_blank">LeetCode题解</a>|
 |0878.第N个神奇数字|困难|<a href="https://leetcode.cn/problems/nth-magical-number/solutions/" target="_blank">题目地址</a>|<a href="https://blog.letmefly.xyz/2022/11/22/LeetCode%200878.%E7%AC%ACN%E4%B8%AA%E7%A5%9E%E5%A5%87%E6%95%B0%E5%AD%97/" target="_blank">题解地址</a>|<a href="https://letmefly.blog.csdn.net/article/details/127978493" target="_blank">CSDN题解</a>|<a href="https://leetcode.cn/problems/nth-magical-number/solutions/1984934/letmefly-878di-n-ge-shen-qi-shu-zi-by-ti-jcvf/" target="_blank">LeetCode题解</a>|
+|0881.救生艇|中等|<a href="https://leetcode.cn/problems/boats-to-save-people/solutions/" target="_blank">题目地址</a>|<a href="https://blog.letmefly.xyz/2024/06/10/LeetCode%200881.%E6%95%91%E7%94%9F%E8%89%87/" target="_blank">题解地址</a>|<a href="https://letmefly.blog.csdn.net/article/details/139582336" target="_blank">CSDN题解</a>|<a href="https://leetcode.cn/problems/boats-to-save-people/solutions/2806923/letmefly-881jiu-sheng-ting-pai-xu-shuang-ik77/" target="_blank">LeetCode题解</a>|
 |0886.可能的二分法|中等|<a href="https://leetcode.cn/problems/possible-bipartition/" target="_blank">题目地址</a>|<a href="https://blog.letmefly.xyz/2022/10/16/LeetCode%200886.%E5%8F%AF%E8%83%BD%E7%9A%84%E4%BA%8C%E5%88%86%E6%B3%95/" target="_blank">题解地址</a>|<a href="https://letmefly.blog.csdn.net/article/details/127344544" target="_blank">CSDN题解</a>|<a href="https://leetcode.cn/problems/possible-bipartition/solution/letmefly-886ke-neng-de-er-fen-fa-tu-sou-zmnxe/" target="_blank">LeetCode题解</a>|
 |0889.根据前序和后序遍历构造二叉树|中等|<a href="https://leetcode.cn/problems/construct-binary-tree-from-preorder-and-postorder-traversal/solutions/" target="_blank">题目地址</a>|<a href="https://blog.letmefly.xyz/2024/02/22/LeetCode%200889.%E6%A0%B9%E6%8D%AE%E5%89%8D%E5%BA%8F%E5%92%8C%E5%90%8E%E5%BA%8F%E9%81%8D%E5%8E%86%E6%9E%84%E9%80%A0%E4%BA%8C%E5%8F%89%E6%A0%91/" target="_blank">题解地址</a>|<a href="https://letmefly.blog.csdn.net/article/details/136227823" target="_blank">CSDN题解</a>|<a href="https://leetcode.cn/problems/construct-binary-tree-from-preorder-and-postorder-traversal/solutions/2649414/letmefly-889gen-ju-qian-xu-he-hou-xu-bia-9yfs/" target="_blank">LeetCode题解</a>|
 |0891.子序列宽度之和|困难|<a href="https://leetcode.cn/problems/sum-of-subsequence-widths/solutions/" target="_blank">题目地址</a>|<a href="https://blog.letmefly.xyz/2022/11/18/LeetCode%200891.%E5%AD%90%E5%BA%8F%E5%88%97%E5%AE%BD%E5%BA%A6%E4%B9%8B%E5%92%8C/" target="_blank">题解地址</a>|<a href="https://letmefly.blog.csdn.net/article/details/127916253" target="_blank">CSDN题解</a>|<a href="https://leetcode.cn/problems/sum-of-subsequence-widths/solutions/1977812/letmefly-891zi-xu-lie-kuan-du-zhi-he-by-ttj8r/" target="_blank">LeetCode题解</a>|

README.md

@@ -0,0 +1,161 @@
+---
+title: 881.救生艇
+date: 2024-06-10 21:00:04
+tags: [题解, LeetCode, 中等, 贪心, 数组, 双指针, 排序]
+---
+
+# 【LetMeFly】881.救生艇：排序+双指针（大人掌船，能捎就捎）
+
+力扣题目链接：[https://leetcode.cn/problems/boats-to-save-people/](https://leetcode.cn/problems/boats-to-save-people/)
+
+<p>给定数组<meta charset="UTF-8" />&nbsp;<code>people</code>&nbsp;。<code>people[i]</code>表示第 <code>i</code><sup>&nbsp;</sup>个人的体重&nbsp;，<strong>船的数量不限</strong>，每艘船可以承载的最大重量为&nbsp;<code>limit</code>。</p>
+
+<p>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&nbsp;<code>limit</code>。</p>
+
+<p>返回 <em>承载所有人所需的最小船数</em>&nbsp;。</p>
+
+<p>&nbsp;</p>
+
+<p><strong>示例 1：</strong></p>
+
+<pre>
+<strong>输入：</strong>people = [1,2], limit = 3
+<strong>输出：</strong>1
+<strong>解释：</strong>1 艘船载 (1, 2)
+</pre>
+
+<p><strong>示例 2：</strong></p>
+
+<pre>
+<strong>输入：</strong>people = [3,2,2,1], limit = 3
+<strong>输出：</strong>3
+<strong>解释：</strong>3 艘船分别载 (1, 2), (2) 和 (3)
+</pre>
+
+<p><strong>示例 3：</strong></p>
+
+<pre>
+<strong>输入：</strong>people = [3,5,3,4], limit = 5
+<strong>输出：</strong>4
+<strong>解释：</strong>4 艘船分别载 (3), (3), (4), (5)</pre>
+
+<p>&nbsp;</p>
+
+<p><strong>提示：</strong></p>
+
+<ul>
+	<li><code>1 &lt;= people.length &lt;= 5 * 10<sup>4</sup></code></li>
+	<li><code>1 &lt;= people[i] &lt;= limit &lt;= 3 * 10<sup>4</sup></code></li>
+</ul>
+
+
+    
+## 解题方法：排序+双指针
+
+### 具体做法
+
+首先对所有人按体重从低到高排序。
+
+使用两个指针$l$和$r$分别指向数组的第一个和最后一个元素。
+
+每次$r$指针向前移动一个元素（并且救生艇数量加一），另外的，若$r$指针移动前$people[l]+people[r]\leq lmit$，则$l$指针右移一个元素（相当于大人捎个小孩）。
+
+### 为什么这么做
+
+**为什么r指针每次都移动而l指针不一定移动？**
+
+反正每个人都得坐船走，可以理解为先分配大人（每次r左移），若此大人还能捎带一个小孩儿，则就把这个小孩儿带走（此时l右移）。
+
+**大人不应该带上“尽可能重的小孩”吗？**
+
+第一反应是这样的。对于大人$people[r]$，是否应该带上满足$people[i]+people[r]\leq limit$的最大$i$而不是剩下所有小孩中最小的$l$呢？
+
+其实带谁都一样。反正都是一个人头。此时$r$能带上“更重的小孩$i$”，那么待会儿“更轻的大人”也一定能带上小孩$i$。带$l$写起来简单，所以带$l$不带$i$。
+
+### 时空复杂度分析
+
++ 时间复杂度$O(n\log n)$，其中$n=len(people)$
++ 空间复杂度$O(\log n)$
+
+时空复杂度的来源主要是排序。
+
+### AC代码
+
+#### C++
+
+```cpp
+class Solution {
+public:
+    int numRescueBoats(vector<int>& people, int limit) {
+        sort(people.begin(), people.end());
+        int ans = 0;
+        for (int l = 0, r = people.size() - 1; l <= r; ans++, r--) {
+            // 不用特判l是否等于r，因为不影响结果（若l=r则说明就剩一个人了，带不带那个“虚空影子”都无所谓）
+            if (people[l] + people[r] <= limit) {
+                l++;
+            }
+        }
+        return ans;
+    }
+};
+```
+
+#### Go
+
+```go
+// package main
+
+// import "sort"
+
+func numRescueBoats(people []int, limit int) int {
+    sort.Ints(people);
+    ans := 0
+    for l, r := 0, len(people) - 1; l <= r; ans, r = ans + 1, r - 1 {
+        if people[l] + people[r] <= limit {
+            l++;
+        }
+    }
+    return ans
+}
+```
+
+#### Java
+
+```java
+// import java.util.Arrays;
+
+class Solution {
+    public int numRescueBoats(int[] people, int limit) {
+        Arrays.sort(people);
+        int ans = 0;
+        for (int l = 0, r = people.length - 1; l <= r; ans++, r--) {
+            if (people[l] + people[r] <= limit) {
+                l++;
+            }
+        }
+        return ans;
+    }
+}
+```
+
+#### Python
+
+```python
+# from typing import List
+
+class Solution:
+    def numRescueBoats(self, people: List[int], limit: int) -> int:
+        people.sort()
+        ans = 0
+        l, r = 0, len(people) - 1
+        while l <= r:
+            if people[l] + people[r] <= limit:
+                l += 1
+            r -= 1
+            ans += 1
+        return ans
+```
+
+> 同步发文于CSDN和我的[个人博客](https://blog.letmefly.xyz/)，原创不易，转载经作者同意后请附上[原文链接](https://blog.letmefly.xyz/2024/06/10/LeetCode%200881.%E6%95%91%E7%94%9F%E8%89%87/)哦~
+>
+> Tisfy：[https://letmefly.blog.csdn.net/article/details/139582336](https://letmefly.blog.csdn.net/article/details/139582336)

Solutions/LeetCode 0881.救生艇.md

@@ -191,7 +191,7 @@ tags: [其他, 知识, 英语, Notes]
 |parachute|n. 降落伞<br/>v. 跳伞，空投|
 |stripe|n. 条纹，臂章|
 |||
-|villain|n. 恶棍，反面人物，罪魁祸首|
+|<font color="#28bea0" title="二次复习">villain</font>|n. 恶棍，反面人物，罪魁祸首|
 |suspense|n. 悬念，焦虑，（对即将发生的事情等）担心，兴奋|
 |||
 |congestion|n. 充血，淤血，(交通)拥塞，塞车|
@@ -245,7 +245,14 @@ tags: [其他, 知识, 英语, Notes]
 |materialize|v. 实现，发生，成为现实，突然显现|
 |serene|adj. 平静的，宁静的，安详的<br/>v. 宁静，<诗>使(海,脸色等)平静，使(天空)明朗<br/>n. 平静(的海)，<诗,古>晴朗(天空)|
 |hazard|n. 危险，危害<br/>冒失地提出，冒险猜测，冒...的风险，使处于危险|
-
+|||
+|soot|n. (煤)烟灰，烟垢<br/>v. 用煤炭覆盖|
+|parade|v. 游行，队列进行，炫耀，展示<br/>n. (庆祝)游行，队列，阅兵进行，炫耀，展示|
+|||
+|enchant|v. 使着迷，使陶醉，对...施魔法/念咒语|
+|mathematician|n. 数学家|
+|inn|n. 客栈，(乡村可夜宿的)小酒店<br/>v. 住旅馆|
+|flux|n. 不断的变动，不停的变化，通量，流动|
 
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