手动实现STL中的search_n算法，代码如下：

 

#pragma once

#include <iostream>
#include <algorithm>
#include <string>
#include <vector>

using namespace std;


template<typename ForwardIter, typename Integer, typename T>
ForwardIter np_serach_n(
    ForwardIter first,
    ForwardIter last,
    Integer count,
    const T& value)
{
    if (count < 0)
        return first;


    first = find(first, last, value);
    while (first != last)
    {
        ForwardIter cur = first;

        cur++;
        int n = count - 1;

        while (cur != last && n != 0 && *cur == value)
        {
            cur++;
            n--;
        }

        if (n == 0)
            return first;
        else
            first = find(cur, last, value);
    }

    return last;
}

template<typename ForwardIter, typename Integer, typename T, typename BinaryPred>
ForwardIter np_serach_n(
    ForwardIter first,
    ForwardIter last,
    Integer count,
    const T& value,
    BinaryPred binary_pred)
{
    if (count < 0)
        return first;

    while (first != last && !binary_pred(*first, value))
        ++first;

    while (first != last)
    {
        ForwardIter cur = first;
        ++cur;

        Integer n = count - 1;

        while (cur != last && n != 0 && binary_pred(*cur, value)) {
            cur++;
            n--;
        }

        if (n == 0)
            return first;
        else
        {
            first = cur;
            while (first != last && !binary_pred(*first, value))
                ++first;
        }
    }

    return last;
}

 

 

调用方法：

 

// Neptune.cpp: 定义应用程序的入口点。
//

#include "Neptune.h"
#include "non_mutate.h"
#include <functional>

void test_np_search_n()
{
    int count = 2;
    string number = "world";

    vector<string> numbers{ "Hello", "world", "world", "I", "love", "you", "world" };

    auto it = np_serach_n<decltype(numbers.cbegin()), decltype(count), decltype(number)>(
        numbers.cbegin(), numbers.cend(), count, number);


    if (it != numbers.cend())
    {
        cout << "Find " << count << " " << number << " index is: " << it - numbers.cbegin();
    }
    else
    {
        cout << "Can't find " << count << " " << number;
    }

}


void test_np_serach_n_predicat(int count = 2)
{
    //int number = 4;
    //vector<int> data{ 1, 3, 4, 5, 2, 1, 7, 8, 9 };
    std::string number("hellooo");
    vector<decltype(number)> data {"hello", "world", "chris", "I", "love", "you"};

    
    std::function<bool(decltype(*data.cbegin()), decltype(number))>  Predicate;

    auto it = np_serach_n<decltype(data.cbegin()), decltype(count), decltype(number), decltype(Predicate)>(
        data.cbegin(),
        data.cend(),
        count,
        number,
        [](decltype(*data.cbegin()) a, decltype(number) b) -> bool {
            return b.length() - a.length() > 2;
        });

    if (it != data.cend())
    {
        cout << "Find " << count << " index is: " << it - data.cbegin();
    }
    else
    {
        cout << "Can't find! ";
    }
}

int main()
{
    test_np_search_n();
    test_np_serach_n_predicat();
    return 0;
}