c/c++:STL之Binary search

STL之Binary search

http://www.cppblog.com/patriking/archive/2011/01/16/138617.html

    STL中对于有序序列（vector,list等）提供了相当相当强大的二分搜索Binary search算法。对于可以随机访问容器（如vector等），binary search负载度为对数级别（LogN)，对于非随机访问容器（如list），则算法复杂度为线性。现在简要介绍一下几种常用的binary search算法：

ForwardIterator lower_bound (ForwardIterator first,ForwardIterator last, const T& value)
ForwardIterator lower_bound (ForwardIterator first,ForwardIterator last, const T& value, Compare comp)
//查找最远的一个iterator i， 使得[first,i)里面的任意一个iterator j，有 *j < value or comp(*j,value)==true. 

ForwardIterator upper_bound (ForwardIterator first,ForwardIterator last, const T& value)
ForwardIterator upper_bound (ForwardIterator first,ForwardIterator last, const T& value, Compare comp)
//查找最远的一个iterator i， 使得[first,i)里面的任意一个iterator j，有 !(*j < value) or comp(*j,value)==false. 

pair equal_range(ForwardIterator first, ForwardIterator last, const T& value)
pair equal_range(ForwardIterator first, ForwardIterator last, const T& value, Compare comp)
//查找最大的subrange[i,j)，使得任意一个iterator in [i,j)满足!(*k<value) && !(value<*k) or comp(*k,value)==false && comp(value,*k)==false.

bool binary_search (ForwardIterator first, ForwardIterator last, const T& value)
bool binary_search (ForwardIterator first, ForwardIterator last, const T& value, Compare comp)
// 查找是否在[first,last)中存在iterator i,满足 !(*i<value) && !(value<*i) or comp(*i,value)==false && comp(value,*i)==false
// 存在则返回true,否则返回false.  

#include<algorithm>
#include<iostream>
#include<vector>
#include<iterator>
using namespace std;
int main()
{
    vector<int>v;
    vector<int>::iterator itr;
    pair< vector<int>::iterator, vector<int>::iterator >vecpair;
    
    for(int i = 1; i <= 20; i++){
        v.push_back(i%6);
    }
    sort(v.begin(),v.end());
    cout << "array: " << endl << "    ";
    copy(v.begin(),v.end(),ostream_iterator<int>(cout," "));
    cout << endl;
    
    //lower_bound
    cout << "lower_bound function, value = 3:" << endl; 
    itr = lower_bound(v.begin(),v.end(),3);
    cout << "    [first, itr) = ";
    copy(v.begin(),itr,ostream_iterator<int>(cout," "));
    cout << endl;
    cout << "    [itr, last) = ";
    copy(itr,v.end(),ostream_iterator<int>(cout," "));
    cout << endl << endl;
    
    // upper_bound
    cout << "upper_bound function, value = 3:" << endl; 
    itr = upper_bound(v.begin(),v.end(),3);
    cout << "    [first, itr) = ";
    copy(v.begin(),itr,ostream_iterator<int>(cout," "));
    cout << endl;
    cout << "    [itr, last) = ";
    copy(itr,v.end(),ostream_iterator<int>(cout," "));
    cout << endl << endl;
    
    // equal_range
    cout << "equal_range function, value = 3:" << endl; 
    vecpair = equal_range(v.begin(),v.end(),3);
    
    cout << "    [vecpair->first, vecpair->second) = ";
    copy(vecpair.first, vecpair.second, ostream_iterator<int>(cout," "));
    cout << endl << endl;
    
    //binary_search, value = 3
    cout << "binary_search function, value = 3:" << endl;
    cout << "3 is " << (binary_search(v.begin(),v.end(),3) ? "":"not ") << "in array." << endl;
    cout << endl;
    
    //binary_search, value = 6
    cout << "binary_search function, value = 6:" << endl;
    cout << "6 is " << (binary_search(v.begin(),v.end(),6) ? "":"not ") << "in array." << endl;
    cout << endl;
    
    return 0;    
}

 

 

array:
    0 0 0 1 1 1 1 2 2 2 2 3 3 3 4 4 4 5 5 5
lower_bound function, value = 3:
    [first, itr) = 0 0 0 1 1 1 1 2 2 2 2
    [itr, last) = 3 3 3 4 4 4 5 5 5

upper_bound function, value = 3:
    [first, itr) = 0 0 0 1 1 1 1 2 2 2 2 3 3 3
    [itr, last) = 4 4 4 5 5 5

equal_range function, value = 3:
    [vecpair->first, vecpair->second) = 3 3 3

binary_search function, value = 3:
3 is in array.

binary_search function, value = 6:
6 is not in array.