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std::max_element

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< cpp‎ | algorithm

 
 
アルゴリズムライブラリ
機能します
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Functions
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シーケンス動作を非改変
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Non-modifying sequence operations
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シーケンス動作を変更する
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Modifying sequence operations
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操作を仕切る
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Partitioning operations
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(ソートされた範囲で)ソート操作
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Sorting operations (on sorted ranges)
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バイナリ検索操作(ソート範囲で)
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Binary search operations (on sorted ranges)
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(ソートされた範囲で)操作を設定します
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Set operations (on sorted ranges)
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ヒープ操作
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Heap operations
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最小値/最大値操作
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Minimum/maximum operations
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max
max_element
min
min_element
minmax(C++11)
minmax_element(C++11)
数値演算
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Numeric operations
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Cライブラリ
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C library
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Defined in header <algorithm>
template< class ForwardIt >
ForwardIt max_element( ForwardIt first, ForwardIt last );
(1)
template< class ForwardIt, class Compare >
ForwardIt max_element( ForwardIt first, ForwardIt last, Compare comp );
(2)

Finds the greatest element in the range [first, last). The first version uses operator< to compare the values, the second version uses the given comparison function comp.

目次

[編集] パラメータ

first, last -
検討する範囲を定義前方反復子
Original:
forward iterators defining the range to examine
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cmp - 比較関数. if *a is less than *b 場合、 ​trueを返します.

比較関数のシグネチャは以下と同等でなければなりません.

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

シグネチャはconstを含まなくても構いませんが, 比較関数は渡されたオブジェクトを変更してはなりません.
The types Type1 and Type2 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to both of them. ​

型の要件
-
ForwardItForwardIterator

の要求を満足しなければなりません。

[編集] 値を返します

Iterator to the greatest element in the range [first, last). If several elements in the range are equivalent to the greatest element, returns the iterator to the first such element. Returns last if the range is empty.

[編集] 複雑

まさにmax(N-1,0)比較、どこN = std::distance(first, last).
Original:
Exactly max(N-1,0) comparisons, where N = std::distance(first, last).
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[編集] 可能な実装

First version
template<class ForwardIt>
ForwardIt max_element(ForwardIt first, ForwardIt last)
{
    if (first == last) {
        return last;
    }
    ForwardIt largest = first;
    ++first;
    for (; first != last; ++first) {
        if (*largest < *first) {
            largest = first;
        }
    }
    return largest;
}
Second version
template<class ForwardIt, class Compare>
ForwardIt max_element(ForwardIt first, ForwardIt last, 
                            Compare comp)
{
    if (first == last) {
        return last;
    }
    ForwardIt largest = first;
    ++first;
    for (; first != last; ++first) {
        if (comp(*largest, *first)) {
            largest = first;
        }
    }
    return largest;
}

[編集]

#include <algorithm>
#include <iostream>
#include <vector>
#include <cmath>
 
static bool abs_compare(int a, int b)
{
    return (std::abs(a) < std::abs(b));
}
 
int main()
{
    std::vector<int> v{ 3, 1, -14, 1, 5, 9 }; 
    std::vector<int>::iterator result;
 
    result = std::max_element(v.begin(), v.end());
    std::cout << "max element at: " << std::distance(v.begin(), result) << '\n';
 
    result = std::max_element(v.begin(), v.end(), abs_compare);
    std::cout << "max element (absolute) at: " << std::distance(v.begin(), result);
}

出力:

max element at: 5
max element (absolute) at: 2

[編集] も参照してください

範囲内の最小の要素を返します
Original:
returns the smallest element in a range
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(関数テンプレート) [edit]
範囲内の最小と最大の要素を返します
Original:
returns the smallest and the largest element in a range
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(関数テンプレート) [edit]
二つの要素のうちの大きい方を返します
Original:
returns the larger of two elements
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(関数テンプレート) [edit]