常用库函数

1.reverse和unique

#include<algorithm>
#include<iostream>
#include<vector>
using namespace std;
int main()
{
    vector<int> v({1,2,3,4,5,5});
    reverse(v.begin(),v.end());//O(n)
    for(auto x:v) cout<<x<<" ";
    cout<<endl;
    int a[]={1,2,2,3,3};
    //unique会对相同元素在一起的去重
    int m=unique(a,a+5)-a;cout<<m<<endl;
    //m为地址间的差值
    for(int i=0;i<m;++i) cout<<a[i]<<" ";
    cout<<endl;
    m=unique(v.begin(),v.end())-v.begin();cout<<m<<endl;
    v.erase(unique(v.begin(),v.end()),v.end());
    for(auto x:v) cout<<x<<" ";
}

2.random_shuffle

#include<algorithm>
#include<iostream>
#include<vector>
#include<ctime>
using namespace std;
int main()
{
    srand(time(0));
    int a[]={1,2,3,4,5};
    random_shuffle(a,a+5);
    for(auto x:a) cout<<x<<" ";
}

3.sort

#include<algorithm>
#include<iostream>
#include<vector>
#include<ctime>
struct st{
   int a,b;
   //重载运算可以看作当前结构体是否排在x前面
   bool operator < (const st x) const{
      return a>x.a;
   }
}s[2];
bool cmp(int a,int b)//cmp可以看作a是否应该排在b的前面
{
    return (a%2)&&!(b%2);
}
using namespace std;
int main()
{
    s[0]={1,2};
    s[1]={2,1};
    sort(s,s+2);
    cout<<s[0].a<<" "<<s[0].b<<endl;
    int p[]={1,2,3,4,5};
    sort(p,p+5,cmp);//cmp实现了将奇数排在偶数前
    for(auto x:p) cout<<x<<" ";
}

4.upper_bound和lower_bound

#include<iostream>
#include<algorithm>
using namespace std;
int main()
{

    int a[]={1,2,4,5};
    int *p=lower_bound(a,a+4,2);
    int *q=upper_bound(a,a+4,2);
    cout<<*p<<" "<<*q<<endl;
    int m=p-a,n=q-a;
    cout<<m<<" "<<n<<endl;//得到下标
    cout<<q-p<<endl;//得到2出现的次数
}