find_if函数与partition函数的转换

编写程序，求大于等于一个给定长度的单词有多少。我们还会修改输出，使程序只打印大于等于给定长度的单词。

使用find_if实现的代码如下：

#include<algorithm>

#include<vector>

#include<iostream>

#include<string>

using namespace std;

void biggies(vector<string> &words,vector<string>::size_type sz)

{

    sort(words.begin(),words.end());

    auto end_unique=unique(words.begin(),words.end());

    words.erase(end_unique,words.end());

    stable_sort(words.begin(),words.end(),[](const string &s1,const string s2) {return s1.size()<s2.size();});

    auto wc=find_if(words.begin(),words.end(),[sz](const string &s) { return s.size()>=sz;});

    auto count=words.end()-wc;

    cout<<count<<endl;

    for_each(wc,words.end(),[](const string &s) {cout<<s<<" ";});

    cout<<endl;

}

int main()

{

    vector<string> words={"aaaaa","aaaaaaa","dfdaaaa","fdaa","aaa","dfaaaaa"};

    biggies(words,);

    return ;

}

使用partition代码的程序：

#include<algorithm>

#include<vector>

#include<iostream>

#include<string>

using namespace std;

void biggies(vector<string> &words,vector<string>::size_type sz)

{

    sort(words.begin(),words.end());

    auto end_unique=unique(words.begin(),words.end());

    words.erase(end_unique,words.end());

    stable_sort(words.begin(),words.end(),[](const string &s1,const string s2) {return s1.size()<s2.size();});

    auto wc=partition(words.begin(),words.end(),[sz](const string &s) { return s.size()>=sz;});

    auto count=wc-words.begin();

    cout<<count<<endl;

    for_each(words.begin(),wc,[](const string &s) {cout<<s<<" ";});

    cout<<endl;

}

int main()

{

    vector<string> words={"aaaaa","aaaaaaa","dfdaaaa","fdaa","aaa","dfaaaaa"};

    biggies(words,);

    return ;

}

运行结果：

dfdaaaa dfaaaaa aaaaa aaaaaaa

当使用stable_partition后程序：

#include<algorithm>

#include<vector>

#include<iostream>

#include<string>

using namespace std;

void biggies(vector<string> &words,vector<string>::size_type sz)

{

    sort(words.begin(),words.end());

    auto end_unique=unique(words.begin(),words.end());

    words.erase(end_unique,words.end());

    stable_sort(words.begin(),words.end(),[](const string &s1,const string s2) {return s1.size()<s2.size();});

    for_each(words.begin(),words.end(),[](const string &s) {cout<<s<<" ";});

    cout<<endl;

    auto wc=stable_partition(words.begin(),words.end(),[sz](const string &s) { return s.size()>=sz;});

    auto count=wc-words.begin();

    cout<<count<<endl;

    for_each(words.begin(),wc,[](const string &s) {cout<<s<<" ";});

    cout<<endl;

}

int main()

{

    vector<string> words={"aaaaa","aaaaaaa","dfdaaaa","fdaa","aaa","dfaaaaa"};

    biggies(words,);

    return ;

}

运行结果：

aaa fdaa aaaaa aaaaaaa dfaaaaa dfdaaaa 

aaaaa aaaaaaa dfaaaaa dfdaaaa

说明stable_partiton不改变字典顺序，是稳定的操作。

巴特西

find_if函数与partition函数的转换

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