Some common functions and precautions

next_permutation()

#include<bits/stdc++.h>
using namespace std;
signed main(void)
{
    int a[10]={1,2,3};
    do
    {
        printf("%d%d%d\n",a[0],a[1],a[2]);
    }while(next_permutation(a,a+3));//a[0] To a[2] Full Permutation 
    return 0;
}

fill()

#include<bits/stdc++.h>
using namespace std;
signed main(void)
{
    int a[10];
    fill(a,a+5,3);
    for(int i=0;i<5;i++)
    cout<<a[i]<<" ";
    return 0;
}

sort()

#include<bits/stdc++.h>
using namespace std;
bool cmp(int a,int b)
{
    return a>b;
}
signed main(void)
{
    vector<int> p1;
    p1.push_back(4);
    p1.push_back(2);
    p1.push_back(9);
    sort(p1.begin(),p1.end(),cmp);
    cout<<p1[0]<<" "<<p1[1]<<" "<<p1[2]<<endl;
    return 0;
}
//9 4 2

lower_bound(first,last,val),upper_bound(first,last,val), Both are left closed and right open sections

If it is an array, return the pointer , The container returns an iterator , If the target element is not found , Returns the position where the element should be if it exists ( For other features, see the author's previous lower_bound、upper_bound)

Be careful ： many STL The interval in is left closed and right open , for example sort Yes a[1] To a[n] row          The preface should be written as sort(a+1,a+1+n) wait