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C++STL常用算法合集(上)
- 算法主要是由
<algorithm><functional><numeric>组成 <algorithm>是STL头文件中体积最大的一个，涉及比较、交换、查找、遍历、复制、修改等<numeric>体积很小，只包括几个序列上进行简单数学运算的模板函数<functional>定义了一些模板类，用以声明模板函数
一、常用遍历算法
一、for_each
#include<algorithm> #include<iostream> #include<vector> using namespace std; void print1(int val) { cout << val << " "; } class print2 { public: void operator()(int val) { cout << val << " "; } }; void test01() { vector<int>v; for (int i = 0; i < 10; i++) v.push_back(i); for_each(v.begin(), v.end(), print1); cout << endl; for_each(v.begin(), v.end(), print2()); cout << endl; }- 1
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使用普通函数和仿函数作为操作函数，for_each遍历容器
二、transform
class Transform { public: int operator()(int n) { return n+100; } }; void test02() { vector<int>v; for (int i = 0; i < 10; i++) v.push_back(i); vector<int>vTarget; vTarget.resize(v.size()); transform(v.begin(), v.end(), vTarget.begin(), Transform()); for_each(vTarget.begin(), vTarget.end(), print2()); cout << endl; }- 1
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定义仿函数提供transform的操作函数，将v的值+100转移到vTarget上，一定要事先开辟空间
二、常用查找算法
find:查找元素
find_if:按条件查找元素
adjacent_find:查找相邻重复元素
binary_search二分查找法
count:统计元素个数
count_if:按条件统计元素个数一、find
- 查找指定元素，找到返回元素的迭代器，找不到返回结束迭代器位置
#include<iostream> #include<algorithm> #include<vector> #include<string> using namespace std; void test01() { vector<int>v; for (int i = 0; i < 10; i++) v.push_back(i); auto pos=find(v.begin(), v.end(),5); if (pos != v.end()) cout << "找到了:" << *pos << endl; else cout << "没找到" << endl; } class Person { public: string m_name; int m_age; Person(string name, int age) { this->m_age = age; this->m_name = name; } bool operator==(const Person&p) { if (this->m_age == p.m_age&&this->m_name == p.m_name) return true; else return false; } }; void test02() { vector<Person>v; Person p[4] = { {"a",11},{"b",22},{"c",33},{"d",44} }; for (int i = 0; i < 4; i++) v.push_back(p[i]); auto pos = find(v.begin(), v.end(), p[1]); if (pos != v.end()) cout << "找到了,姓名:" << pos->m_name << " 年龄:"<<pos->m_age<<endl; else cout << "没找到" << endl; } int main() { test01(); test02(); }- 1
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通过源码可以看到查找时会有值的比较，对于自定义数据类型需要重载==,否则无法比较
二、find_if
#include<iostream> #include<vector> #include<algorithm> #include<string> using namespace std; class Five { public: bool operator()(int n) { return n > 5; } }; void test01() { vector<int>v; for (int i = 0; i < 10; i++) v.push_back(i); auto pos = find_if(v.begin(), v.end(), Five()); if (pos != v.end()) cout << "找到了:" << *pos << endl; else cout << "没找到" << endl; } class Person { public: string m_name; int m_age; Person(string name, int age) { this->m_age = age; this->m_name = name; } }; class Twenty { public: bool operator()(const Person&p) { return p.m_age > 20; } }; void test02() { vector<Person>v; Person p[4] = { {"aaa",10},{"bbb",20},{"ccc",30},{"ddd",40} }; for (int i = 0; i < 4; i++) v.push_back(p[i]); auto pos=find_if(v.begin(), v.end(), Twenty()); if(pos != v.end()) cout << "找到了,姓名:" << pos->m_name << " 年龄:"<<pos->m_age<<endl; else cout << "没找到" << endl; } int main() { test01(); test02(); return 0; }- 1
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使用与find一样，只不过是查找方法变成了仿函数设置条件，或者函数。三、adjacent_find
#include<iostream> #include<algorithm> #include<vector> using namespace std; void test01() { vector<int>v; v.push_back(0); v.push_back(2); v.push_back(0); v.push_back(3); v.push_back(1); v.push_back(4); v.push_back(3); v.push_back(3); auto pos = adjacent_find(v.begin(), v.end()); if (pos == v.end()) cout << "为找到相邻元素" << endl; else cout << "找到相邻重复元素:" << *pos << endl; }- 1
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返回值是第一个找到的有相邻重复元素的迭代器
四、binary_search
二分查找，效率很高，但要注意的的是，查找的数据必须是有序存储的
其返回值是一个bool类型的值，找到返回true,反之falsevoid test02() { vector<int>v; for (int i = 0; i < 10; i++) v.push_back(i); bool ret=binary_search(v.begin(), v.end(), 7); if (ret) cout << "找到了" << endl; else cout << "没找到" << endl; }- 1
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五、count
统计元素个数
#include<iostream> #include<algorithm> #include<vector> #include<string> using namespace std; void test01() { vector<int>v; for (int i = 0; i <= 573; i++) v.push_back(i); v.push_back(33); v.push_back(33); v.push_back(7); int n1 = count(v.begin(), v.end(), 1), n2 = count(v.begin(), v.end(), 7), n3 = count(v.begin(), v.end(), 33); cout << "1的个数:" << n1 << endl << "7的个数:" << n2 << endl << "33的个数:" << n3 << endl; } class Person { public: int m_age; string m_name; Person(int age, string name) { this->m_age = age; this->m_name = name; } bool operator==(const Person&p) { return this->m_age == p.m_age; } }; void test02() { vector<Person>v; Person p[5]= { {10,"猪猪侠"}, {10,"Tom and Jerry"}, {10,"光头强"}, {20,"星游记"}, {30,"快乐星猫"} }; for (int i = 0; i < 5; i++) v.push_back(p[i]); Person s(10, "喜羊羊"); int num=count(v.begin(), v.end(), s); cout << "和喜羊羊同岁数的人员个数为:" << num << endl; } int main() { test01(); test02(); return 0; }- 1
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同样对于自定义数据类型的计数需要重载==设置判断条件六、count_if
就是把查找的标准从相等匹配换为一个条件判断
#include<iostream> #include<algorithm> #include<vector> #include<string> using namespace std; class Person { public: int m_age; string m_name; Person(int age, string name) { this->m_age = age; this->m_name = name; } }; class cmp1 { public: bool operator()(int val) { return val > 5; } }; class cmp2 { public: bool operator()(const Person&p) { return p.m_age > 10; } }; void test01() { vector<int>v; for (int i = 0; i < 10; i++) v.push_back(i); int n1 = count_if(v.begin(), v.end(), cmp1()); cout << "大于5的值的个数:" << n1; cout << endl; vector<Person>vp; Person p[5] = { {10,"猪猪侠"}, {10,"Tom and Jerry"}, {10,"光头强"}, {20,"星游记"}, {30,"快乐星猫"} }; for (int i = 0; i < 5; i++) vp.push_back(p[i]); int n2 = count_if(vp.begin(), vp.end(), cmp2()); cout << "年龄大于10的人员个数为:" << n2 << endl; } int main() { test01(); return 0; }- 1
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三、常用排序算法
sort:对容器内元素排序
random_shuffle:洗牌，指定范围内的元素随机调整次序
merge:容器元素合并，并存储到另一容器中
reverse:反转指定范围内的元素一、sort
#include<iostream> #include<algorithm> #include<vector> using namespace std; void Print(int val) { cout << val << " "; } class cmp { public: bool operator()(int v1, int v2) { return v1 > v2; } }; void test01() { vector<int>v; for (int i = 0; i < 5; i++) v.push_back(i); sort(v.begin(), v.end()); for_each(v.begin(), v.end(), Print); cout << endl; sort(v.begin(), v.end(), cmp()); for_each(v.begin(), v.end(), Print); cout << endl; }- 1
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可以使用仿函数指定排序方式
二、random_shuffle
随机调整设定范围内数据的顺序
需要设置时间戳srand((unsigned int)time(NULL))保证随机数的有效性#include<time.h> void test02() { vector<int>v; for (int i = 0; i < 10; i++) v.push_back(i); random_shuffle(v.begin(), v.end()); for_each(v.begin(), v.end(),Print); cout << endl; } int main() { srand((unsigned int)time(NULL)); //test01(); test02(); }- 1
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三、merge
合并的两个容器必须有序
同时注意，将存储合并值的容器要有足够的空间去容纳。void test03() { vector<int>v1; vector<int>v2; for (int i = 0; i < 10; i++) { v1.push_back(i); v2.push_back(i*i); } vector<int>vTarget; vTarget.resize(v1.size() + v2.size()); merge(v1.begin(), v1.end(), v2.begin(), v2.end(), vTarget.begin()); for_each(vTarget.begin(), vTarget.end(), Print); }- 1
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这里的合并不是相加合并而是将两块数据有序合并到一块空间上四、reverse
void test04() { vector<int>v; for (int i = 10; i < 100; i += 10) v.push_back(i); cout << "反转前:" << endl; for_each(v.begin(), v.end(), Print); cout << endl; cout << "反转后:" << endl; reverse(v.begin(),v.end()); for_each(v.begin(), v.end(), Print); cout << endl; }- 1
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对指定区间内的数据进行逆序
- 算法主要是由
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- 原文地址：https://blog.csdn.net/qwer1234mnbv_/article/details/125612412