set - 有序集合 | 红黑树

C++之STL整理（4）之set 用法（创建、赋值、增删查改）详解

基本使用

输入

3 1 2 9 1 5 1 6 5 4

代码

#include <bits/stdc++.h>
using namespace std;

int main() {
    set<int> asc;  // 默认递增排序
    set<int, greater<int>> desc;
    set<int>::iterator itlow, itup;

    for(int i = 0; i < 10; i++) {
        int a;
        cin >> a;
        asc.insert(a);
        desc.insert(a);
    }

    for (auto& i : asc) cout << i << " ";
    cout << endl;
    for (auto& i : desc) cout << i << " ";
    cout << endl;

    // 使用lower_bound、upper_bound的前提是序列是有序的！！！
    itlow = asc.lower_bound(3);
    itup = asc.upper_bound(6);
    cout << "The lower bound of 3 in asc (大于等于3的最小数): " << *itlow << endl;
    cout << "The upper bound of 6 in asc (大于6的最小数): " << *itup << endl;


    vector<int> aa = {2, 5, 6, 8, 9, 12};
    vector<int>::iterator vitlow, vitup;
    vitlow = lower_bound(aa.begin(), aa.end(), 6);
    vitup = upper_bound(aa.begin(), aa.end(), 8);
    // vector支持随机访问，可以用“vitlow - aa.begin()”获取元素下标；
    // 但是set不支持随机存取，所以不能通过iterator获取元素下标
    cout << "The index of 6 in aa: " << vitlow - aa.begin() << endl;
    cout << "The upper bound of 8 in aa: " << *vitup << endl;

    return 0;
}

输出

1 2 3 4 5 6 9 
9 6 5 4 3 2 1 
The lower bound of 3 in asc (大于等于3的最小数): 3
The upper bound of 6 in asc (大于6的最小数): 9
The index of 6 in aa: 2
The upper bound of 8 in aa: 9

find - 查找元素

代码

// find example
#include <iostream>     // std::cout
#include <algorithm>    // std::find
#include <vector>       // std::vector

int main () {
  // using std::find with array and pointer:
  int myints[] = { 10, 20, 30, 40 };
  int * p;

  p = std::find (myints, myints+4, 30);
  if (p != myints+4)
    std::cout << "Element found in myints: " << *p << '\n';
  else
    std::cout << "Element not found in myints\n";

  // using std::find with vector and iterator:
  std::vector<int> myvector (myints,myints+4);
  std::vector<int>::iterator it;

  it = find (myvector.begin(), myvector.end(), 30);
  if (it != myvector.end())
    std::cout << "Element found in myvector: " << *it << '\n';
  else
    std::cout << "Element not found in myvector\n";

  return 0;
}