std::lower_bound

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算法库
功能
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Functions
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修改序列操作
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Non-modifying sequence operations
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all_of
any_of
none_of
(C++11)
(C++11)
(C++11)
for_each
count
count_if
mismatch
equal
修改序列操作
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Modifying sequence operations
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分区操作
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Partitioning operations
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is_partitioned(C++11)
partition
partition_copy(C++11)
排序操作(排序的区间)
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Sorting operations (on sorted ranges)
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is_sorted(C++11)
is_sorted_until(C++11)
sort
二进制搜索操作(排序的区间)
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Binary search operations (on sorted ranges)
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lower_bound
upper_bound
设置操作(排序的区间)
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Set operations (on sorted ranges)
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堆的操作
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Heap operations
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最小/最大操作
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Minimum/maximum operations
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数字操作
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Numeric operations
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C库
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C library
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Defined in header <algorithm>
template< class ForwardIt, class T >
ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value );
(1)
template< class ForwardIt, class T, class Compare >
ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value, Compare comp );
(2)

Returns an iterator pointing to the first element in the range [first, last) that is not less than value. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.

目录

[编辑] 参数

first, last - iterators defining the range to examine
value -
值进行比较的元素
Original:
value to compare the elements to
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comp - comparison function which returns ​true if the first argument is less than the second.

The signature of the comparison function should be equivalent to the following:

bool cmp(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The type  Type1 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to  Type1. The type  Type2 must be such that an object of type T can be implicitly converted to  Type2. ​

Type requirements
-
ForwardIt must meet the requirements of ForwardIterator.

[编辑] 返回值

Iterator pointing to the first element that is not less than value, or last if no such element is found.

[编辑] 复杂性

firstlast之间的距离在对数
Original:
Logarithmic in the distance between first and last
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[编辑] 可能的实现

First version
template<class ForwardIt, class T>
ForwardIt lower_bound(ForwardIt first, ForwardIt last, const T& value)
{
    ForwardIt it;
    std::iterator_traits<ForwardIt>::difference_type count, step;
    count = std::distance(first, last);
 
    while (count > 0) {
        it = first; 
        step = count / 2; 
        std::advance(it, step);
        if (*it < value) {
            first = ++it; 
            count -= step + 1; 
        } else count = step;
    }
    return first;
}
Second version
template<class ForwardIt, class T, class Compare>
ForwardIt lower_bound(ForwardIt first, ForwardIt last, const T& value, Compare comp)
{
    ForwardIt it;
    std::iterator_traits<ForwardIt>::difference_type count, step;
    count = std::distance(first,last);
 
    while (count > 0) {
        it = first;
        step = count / 2;
        std::advance(it, step);
        if (comp(*it, value)),
            first = ++it;
            count -= step + 1;
        } else count = step;
    }
    return first;
}

[编辑] 为例

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
 
int main()
{
    std::vector<int> data = { 1, 1, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 6 };
 
    auto lower = std::lower_bound(data.begin(), data.end(), 4);
    auto upper = std::upper_bound(data.begin(), data.end(), 4);
 
    std::copy(lower, upper, std::ostream_iterator<int>(std::cout, " "));
}

Output:

4 4 4

[编辑] 另请参阅

回报在一个特定的键匹配的元素
Original:
returns range of elements matching a specific key
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(函数模板) [edit]
返回一个迭代器的第一个元素“更大的”超过一定值
Original:
returns an iterator to the first element greater than a certain value
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(函数模板) [edit]