max_element可以用于map或set容器吗
时间: 2024-01-02 20:03:34 浏览: 29
不可以直接使用`max_element`函数来查找`map`或`set`容器中的最大元素。`max_element`函数是针对序列容器(如`vector`、`list`等)的算法,用于查找序列中的最大元素。而`map`和`set`是关联容器,其内部元素按照键值进行有序存储,并不是一个序列。如果你想找到`map`或`set`中的最大元素,你可以使用`rbegin()`和`rend()`方法来获取反向迭代器,并通过比较键值来找到最大元素。
相关问题
unordered_set.find
unordered_set.find()函数是用于在unordered_set容器中搜索指定元素的C++ STL内置函数。它返回一个迭代器,指向找到的元素。如果找不到指定元素,则返回指向unordered_set的end()迭代器。该函数的时间复杂度是平均O(1)。下面是一个示例代码,展示了如何使用unordered_set.find()函数来搜索元素并判断是否存在:
```cpp
#include <iostream>
#include <unordered_set>
#include <string>
using namespace std;
int main() {
unordered_set<string> sampleSet = { "geeks1", "for", "geeks2" };
if (sampleSet.find("geeks1") != sampleSet.end()) {
cout << "element found." << endl;
} else {
cout << "element not found." << endl;
}
return 0;
}
```
在这个示例中,我们创建了一个包含三个字符串的unordered_set(sampleSet)。然后,我们使用find()函数来搜索"geeks1"这个元素。如果找到了,就输出"element found.",否则输出"element not found."。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
#### 引用[.reference_title]
- *1* [C++:哈希,unordered_map和unordered_set](https://blog.csdn.net/zhang_si_hang/article/details/126739994)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v92^chatsearchT3_1"}}] [.reference_item style="max-width: 50%"]
- *2* *3* [【C++】unordered_set中find()用法及代码示例](https://blog.csdn.net/qq_29931565/article/details/124511606)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v92^chatsearchT3_1"}}] [.reference_item style="max-width: 50%"]
[ .reference_list ]
n, k = map(int, input().split())points = set()for i in range(n): x, y = map(int, input().split()) points.add((x, y))dp = [[0] * (max(p[1] for p in points) + 2) for _ in range(max(p[0] for p in points) + 2)]for x, y in points: dp[x][y] = 1for i in range(max(p[0] for p in points), 0, -1): for j in range(max(p[1] for p in points), 0, -1): if (i, j) not in points: dp[i][j] = max(dp[i+1][j], dp[i][j+1])ans = max(max(row) for row in dp)print(ans) 转C++
以下是将 Python 代码转换为等效的 C++ 代码:
```c++
#include <iostream>
#include <set>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
int n, k;
cin >> n >> k;
set<pair<int, int>> points;
for (int i = 0; i < n; i++)
{
int x, y;
cin >> x >> y;
points.insert({x, y});
}
int max_x = max_element(points.begin(), points.end(), [](auto &a, auto &b) { return a.first < b.first; })->first;
int max_y = max_element(points.begin(), points.end(), [](auto &a, auto &b) { return a.second < b.second; })->second;
vector<vector<int>> dp(max_x + 2, vector<int>(max_y + 2));
for (const auto &p : points)
dp[p.first][p.second] = 1;
for (int i = max_x; i >= 1; i--)
{
for (int j = max_y; j >= 1; j--)
{
if (!points.count({i, j}))
{
dp[i][j] = max(dp[i + 1][j], dp[i][j + 1]);
}
}
}
int ans = *max_element(dp[1].begin() + 1, dp[1].end());
cout << ans << endl;
return 0;
}
```