# Algorithm Introduction:

• Sort / / sort the elements in the container
• random_shuffle / / shuffle and randomly adjust the order of elements within the specified range.
• merge / / the container elements are merged and stored in another container.
• reverse / / reverses the elements of the specified range.

# sort

## Function Description:

• Sort the elements in the container

## Function prototype:

• sort(iterator beg, iterator end, _Pred);
• //Find the element by value, find the iterator that returns the specified position, and the iterator that returns the end cannot be found
• //beg start iterator
• //End end iterator
• // _ Pred predicate
```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 sorts from small to large by default
sort(v.begin(), v.end());
for_each(v.begin(), v.end(), myPrint);
cout << endl;

//Sort from large to small
sort(v.begin(), v.end(), greater<int>());
for_each(v.begin(), v.end(), myPrint);
cout << endl;
}```

greater: relational affine function.

Summary: sort is one of the most commonly used algorithms in development and needs to be mastered

# random_shuffle

## Function Description:

• Shuffle: randomly adjust the order of elements within a specified range.
• When adjusting random numbers, you also need a random number seed. It can be added to the main() function or above the call shuffle.

## Function prototype:

• random_shuffle(iterator beg, iterator end);
• //Randomly adjust the order of elements within the specified range
• //beg start iterator
• //End end iterator
```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;

//Disorder order
random_shuffle(v.begin(), v.end());
for_each(v.begin(), v.end(), myPrint());
cout << endl;
}```

Summary: random_shuffle shuffle algorithm is more practical. Remember to add random number seeds when using it

# merge

## Function Description:

• The two container elements are merged and stored in another container.

## Function prototype:

• merge(iterator beg1, iterator end1, iterator beg2, iterator end2, iterator dest);
• //Container elements are merged and stored in another container
• //Note: the two containers must be in order
• //beg1 container 1 start iterator
• //end1 container 1 end iterator
• //beg2 container 2 start iterator
• //end2 container 2 end iterator
• //dest destination container start iterator
```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;
//The target container needs to open up space in advance
vtarget.resize(v1.size() + v2.size());
//Merging requires two ordered sequences
merge(v1.begin(), v1.end(), v2.begin(), v2.end(), vtarget.begin());
for_each(vtarget.begin(), vtarget.end(), myPrint());
cout << endl;
}```

Summary: the two containers merged by merge must be an ordered sequence. After merging, they are still an ordered sequence. The target container needs to open up space in advance.

# reverse

## Function Description:

• Invert the elements in the container. Head to tail.

## Function prototype:

• reverse(iterator beg, iterator end);
• //Inverts the elements of the specified range
• //beg start iterator
• //End end iterator
```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 << "Before reversing: " << endl;
for_each(v.begin(), v.end(), myPrint());
cout << endl;

cout << "After reversal: " << endl;

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

Conclusion: reverse reverses the elements in the interval, which may be involved in the interview question.

Keywords: C++ Algorithm

Added by tommy445 on Wed, 16 Feb 2022 06:48:33 +0200