# 18.3 常用排序算法

**学习目标：**

* 掌握常用的排序算法

**算法简介：**

* `sort` //对容器内元素进行排序
* `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` // 反转指定范围的元素

### **1 sort**

**功能描述：**

* 对容器内元素进行排序

**函数原型：**

* `sort(iterator beg, iterator end, _Pred);`

  // 按值查找元素，找到返回指定位置迭代器，找不到返回结束迭代器位置

  // beg 开始迭代器

  // end 结束迭代器

  // \_Pred 谓词

**示例：**

```
#include <algorithm>
#include <vector>

void myPrint(int val)
{
	cout << val << " ";
}

void test01() {
	vector<int> v;
	v.push_back(10);
	v.push_back(30);
	v.push_back(50);
	v.push_back(20);
	v.push_back(40);

	//sort默认从小到大排序
	sort(v.begin(), v.end());
	for_each(v.begin(), v.end(), myPrint);
	cout << endl;

	//从大到小排序
	sort(v.begin(), v.end(), greater<int>());
	for_each(v.begin(), v.end(), myPrint);
	cout << endl;
}

int main() {

	test01();

	system("pause");

	return 0;
}
```

{% hint style="info" %}
总结：sort属于开发中最常用的算法之一，需熟练掌握
{% endhint %}

### **2 random\_shuffle**

**功能描述：**

* 洗牌 指定范围内的元素随机调整次序

**函数原型：**

* `random_shuffle(iterator beg, iterator end);`

  // 指定范围内的元素随机调整次序

  // beg 开始迭代器

  // end 结束迭代器

**示例：**

```
#include <algorithm>
#include <vector>
#include <ctime>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	srand((unsigned int)time(NULL));
	vector<int> v;
	for(int i = 0 ; i < 10;i++)
	{
		v.push_back(i);
	}
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;

	//打乱顺序
	random_shuffle(v.begin(), v.end());
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;
}

int main() {

	test01();

	system("pause");

	return 0;
}
```

{% hint style="info" %}
总结：random\_shuffle洗牌算法比较实用，使用时记得加随机数种子
{% endhint %}

### **3 merge**

**功能描述：**

* 两个容器元素合并，并存储到另一容器中

**函数原型：**

* `merge(iterator beg1, iterator end1, iterator beg2, iterator end2, iterator dest);`

  // 容器元素合并，并存储到另一容器中

  // 注意: 两个容器必须是**有序的**

  // beg1 容器1开始迭代器\
  // end1 容器1结束迭代器\
  // beg2 容器2开始迭代器\
  // end2 容器2结束迭代器\
  // dest 目标容器开始迭代器

**示例：**

```
#include <algorithm>
#include <vector>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int> v1;
	vector<int> v2;
	for (int i = 0; i < 10 ; i++) 
    {
		v1.push_back(i);
		v2.push_back(i + 1);
	}

	vector<int> vtarget;
	//目标容器需要提前开辟空间
	vtarget.resize(v1.size() + v2.size());
	//合并  需要两个有序序列
	merge(v1.begin(), v1.end(), v2.begin(), v2.end(), vtarget.begin());
	for_each(vtarget.begin(), vtarget.end(), myPrint());
	cout << endl;
}

int main() {

	test01();

	system("pause");

	return 0;
}
```

{% hint style="info" %}
总结：merge合并的两个容器必须的有序序列
{% endhint %}

### **4 reverse**

**功能描述：**

* 将容器内元素进行反转

**函数原型：**

* `reverse(iterator beg, iterator end);`

  // 反转指定范围的元素

  // beg 开始迭代器

  // end 结束迭代器

**示例：**

```
#include <algorithm>
#include <vector>

class myPrint
{
public:
	void operator()(int val)
	{
		cout << val << " ";
	}
};

void test01()
{
	vector<int> v;
	v.push_back(10);
	v.push_back(30);
	v.push_back(50);
	v.push_back(20);
	v.push_back(40);

	cout << "反转前： " << endl;
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;

	cout << "反转后： " << endl;

	reverse(v.begin(), v.end());
	for_each(v.begin(), v.end(), myPrint());
	cout << endl;
}

int main() {

	test01();

	system("pause");

	return 0;
}
```

{% hint style="info" %}
总结：reverse反转区间内元素，面试题可能涉及到
{% endhint %}


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