STL lower_bound upper_bound 用法

1.lower_bound（begin,end,x）

返回第一个>=x的位置，找不到return .end()

2.upper_bound (begin,end,x)

返回第一个>x的位置，找不到return .end()

减掉begin得到下标

vector版

#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<vector> 
using namespace std;
vector<int>a;
int b[10];
int main(){
    
    a.push_back(1);
    a.push_back(1);
    a.push_back(2);
    a.push_back(3);
    int p=lower_bound(a.begin(),a.end(),1)-a.begin();
    int q=lower_bound(a.begin(),a.end(),2)-a.begin();
    printf("%d %d\n",p,q);// 0 2
    
    
    p=upper_bound(a.begin(),a.end(),1)-a.begin();
    q=upper_bound(a.begin(),a.end(),2)-a.begin();
    int r=upper_bound(a.begin(),a.end(),3)-a.begin();
    printf("%d %d %d\n",p,q,r);// 2 3 4
    
    return 0;
}

View Code

数组版

#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<vector> 
using namespace std;
vector<int>a;
int b[4]={1,1,2,3};
int main(){
    int p=lower_bound(b,b+4,1)-b;
    int q=lower_bound(b,b+4,2)-b;
    printf("%d %d\n",p,q);// 0 2
    
    
    p=upper_bound(b,b+4,1)-b;
    q=upper_bound(b,b+4,2)-b;
    int r=upper_bound(b,b+4,3)-b;
    printf("%d %d %d\n",p,q,r);// 2 3 4
    
    return 0;
}

View Code

set (直接返回值)

#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<vector> 
#include<set> 
using namespace std;
multiset<int>s;
int main(){
    s.insert(1);
    s.insert(1);
    s.insert(2);
    s.insert(3);
    set<int>::iterator p=s.lower_bound(1);
    set<int>::iterator q=s.lower_bound(2);
    printf("%d %d\n",*p,*q);// 1 2
    return 0;
}

View Code

来源：https://www.cnblogs.com/liankewei/p/11723157.html

标签

lower_bound

begin

stl