# 18.5 常用集合算法

**学习目标：**

* 掌握常用的算术生成算法

**注意：**

* 算术生成算法属于小型算法，使用时包含的头文件为 `#include <numeric>`

**算法简介：**

* `accumulate` // 计算容器元素累计总和
* `fill` // 向容器中添加元素

  ​

### **1 accumulate**

**功能描述：**

* 计算区间内 容器元素累计总和

**函数原型：**

* `accumulate(iterator beg, iterator end, value);`

  // 计算容器元素累计总和

  // beg 开始迭代器

  // end 结束迭代器

  // value 起始值

**示例：**

```
#include <numeric>
#include <vector>
void test01()
{
	vector<int> v;
	for (int i = 0; i <= 100; i++) {
		v.push_back(i);
	}

	int total = accumulate(v.begin(), v.end(), 0);

	cout << "total = " << total << endl;
}

int main() {

	test01();

	system("pause");

	return 0;
}
```

{% hint style="info" %}
总结：accumulate使用时头文件注意是 numeric，这个算法很实用
{% endhint %}

### **2 fill**

**功能描述：**

* 向容器中填充指定的元素

**函数原型：**

* `fill(iterator beg, iterator end, value);`

  // 向容器中填充元素

  // beg 开始迭代器

  // end 结束迭代器

  // value 填充的值

**示例：**

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

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

void test01()
{

	vector<int> v;
	v.resize(10);
	//填充
	fill(v.begin(), v.end(), 100);

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

int main() {

	test01();

	system("pause");

	return 0;
}
```

{% hint style="info" %}
总结：利用fill可以将容器区间内元素填充为 指定的值
{% endhint %}


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