set(STL)

set的性质

Sets(组) are a type of associative container(容器) in which each element(元素) has to be unique(独特) because the value of the element(元素) identifies(识别) it. The values are stored in a specific(特定) sorted order i.e. either ascending or descending(下降). 解释set不会有重复的东西，即使插入多个重复的东西，那么仍然只会显示一个,而且是有顺序的。

举一个例子来看STL中的函数

// C++ program to demonstrate various functions of
// STL
#include <iostream>
#include <iterator>
#include <set>
using namespace std;

int main()
{
	// empty set container
	set<int, greater<int> > s1;//说明这个是大的在前

	// insert elements in random order
	s1.insert(40);//插入函数
	s1.insert(30);
	s1.insert(60);
	s1.insert(20);
	s1.insert(50);

	// only one 50 will be added to the set
	s1.insert(50);
	s1.insert(10);

	// printing set s1
	set<int, greater<int> >::iterator itr;//迭代器
	cout << "\nThe set s1 is : \n";
	for (itr = s1.begin(); itr != s1.end(); itr++) {
		cout << *itr << " ";
	}
	cout << endl;

	// assigning the elements from s1 to s2
	set<int> s2(s1.begin(), s1.end());//默认从小到大

	// print all elements of the set s2
	cout << "\nThe set s2 after assign from s1 is : \n";
	for (itr = s2.begin(); itr != s2.end(); itr++) {
		cout << *itr << " ";
	}
	cout << endl;

	// remove all elements up to 30 in s2
	cout << "\ns2 after removal of elements less than 30 "
			":\n";
	s2.erase(s2.begin(), s2.find(30));//删去小于三十的
	for (itr = s2.begin(); itr != s2.end(); itr++) {
		cout << *itr << " ";
	}

	// remove element with value 50 in s2
	int num;
	num = s2.erase(50);
	cout << "\ns2.erase(50) : ";
	cout << num << " removed\n";
	for (itr = s2.begin(); itr != s2.end(); itr++) {
		cout << *itr << " ";
	}

	cout << endl;

	// lower bound and upper bound for set s1
	cout << "s1.lower_bound(40) : "
		<< *s1.lower_bound(40) << endl;
		// lower_bound的指的是<=是可以取到
		//upper_bound指的是>是只能取到你想要的更高的一位
	cout << "s1.upper_bound(40) : "
		<< *s1.upper_bound(40) << endl;

	// lower bound and upper bound for set s2
	cout << "s2.lower_bound(40) : "
		<< *s2.lower_bound(40) << endl;
	cout << "s2.upper_bound(40) : "
		<< *s2.upper_bound(40) << endl;

	return 0;
}

结果

The set s1 is : 
60 50 40 30 20 10 

The set s2 after assign from s1 is : 
10 20 30 40 50 60 

s2 after removal of elements less than 30 :
30 40 50 60 
s2.erase(50) : 1 removed
30 40 60 
s1.lower_bound(40) : 40
s1.upper_bound(40) : 30
s2.lower_bound(40) : 40
s2.upper_bound(40) : 60

例题来熟悉

给定一个大小为n的整型数组a，你需要对其按照升序排序并进行去重

输入

第一行：一个整数n。（1≤n≤2×10^5）

第二行：n个整数，表示数组a的所有元素。(−10^9≤ai​≤10^9)，(1≤i≤n）

输出

共一行，输出升序排序且去重后的数组a。

样例输入

8
2 0 2 3 0 7 1 7

样例输出

0 1 2 3 7

ANSWER

#include <algorithm>

#include <cmath>

#include <cstring>

#include <iostream>

#include <map>

#include <queue>

#include <set>

#include <stack>

#include <string>

#include <vector>

using namespace std;

typedef long long ll;

constexpr int N = 1e5 + 10;

void solve() {

  int n;

  cin >> n;

  set<int> st;

  for (int i = 0; i < n; i++) {

    int x;

    cin >> x;

    st.insert(x);

   }

  for (auto& v : st) {

  cout << v << ' ';

  }

}

int main() {

  ios::sync_with_stdio(0);

  cin.tie(0);

  cout.tie(0);

  int a = 1;

  while (a--) {

  solve();

 }

}