C++常用算法总结

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PS:后续添加 没有顺序了 搜到什么看什么吧

非char型数组的复制

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#include<bits/stdc++.h>
using namespace std;
int main()
{
    int a[] = {1,2,3};
    int b[3];
    memcpy(b,a,2*sizeof(int));
    cout << b[0] << b[1] << b[2] << endl;
}

查找子串

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#include<bits/stdc++.h>
using namespace std;
int main()
{
    string s1 = "123";
    string s2 = "23";
    string s3 = "73";
    cout << s1.find(s2) << endl;;
    unsigned int c = s1.find(s3);
    cout << c << endl;
    
    //  如果没找到 发挥特别的指针  npos
   // freopen("in.txt","r",stdin);
}

数据初始化

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#include<bits/stdc++.h>
using namespace std;
#define MAXN 220
void display(int num)
{
    cout << num << " ";
}
int main()
{
    int a[2][5],b[10];
    //fill只能初始化一维数组
    fill(b,b+10,1);
    //fill(a,a+100,1);
    memset(a,0,sizeof(a));
    //for_each(a,a+MAXN,display);

    //数据输出
    cout << "b:" << ":";
    for_each(b,b+10,display);
    cout << endl;

    // cout << a << ":";
    // for_each(a,a+10,display);
    // cout << endl;
}

最大公约数

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//公倍数 两数相乘  除以公约数
#include<bits/stdc++.h>
using namespace std;
int a[40] = {1,2};
int main()
{
    cout << __gcd(12,6);
    //cout << __INT32_MAX__ << endl;
}

1.accumulate求和

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#include<numeric>
#include<iostream>
#include<vector>
using namespace std;
int main()
{
    vector<int> v;
    v.push_back(3);
    v.push_back(5);
    v.push_back(9);
    cout << accumulate(v.begin(),v.end(),0);  //0是累加的初值
}

2. atof 字符串转换为double

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/*
	字符串 类型换成double类型 
*/
#include<iostream> 
#include<algorithm> 
#include<stdlib.h>
using namespace std;
int main()
{
	char a[] = "123" ;
	int b = atof(a);
	cout << b;
}

3. 容器为空 begin和end相等

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#include<vector>
#include<iostream>
using namespace std;
int main()
{
    vector<int> v;
    if(v.begin()==v.end())
    cout << "ok1" << endl;
    v.push_back(4);
    if(v.begin()==v.end())
    cout << "ok2" << endl;
}

4. bitset

可实现十进制和二进制的互换

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#include<iostream>
#include<bitset>
using namespace std;
int main()
{
    bitset<32> a(8);
    cout << a[1] << endl;
    int b;
    b = a.to_ullong();
    cout <<a << " " << b <<endl;
}
​```c
### 5.copy 
​```c
/*
	copy(begin,end,begin)
	将第一个数组的begin至end   赋值到第二个容器begin开始 
*/
#include<iostream> 
#include<algorithm> 
using namespace std;
template <class T>
void print(T x)
{
	cout << x << endl;
} 
int main()
{
	int a[] = {1,2,3,4,5,6,7,8,9} ;
	int b[] = {9,8,7,6,5,4,3,2,1} ;  //
	copy(a,a+5,b);  //复制前五个
	for_each(b,b+9,print<int>);
}

6. count

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/*
	count(begin,end, int)  大于int型的数 
	count_if(begin,end,fun)  自定义函数 
*/

#include<iostream> 
#include<algorithm> 
using namespace std;
template <class T>
void print(T x)
{
	cout << x << endl;
} 

int main()
{
	int a[10] = {1,2,3,4,5,5,7,8,9,10};
	cout << count(a,a+10,10);
	//for_each(a,a+9,print<int>) ;
}

7. erase()

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#include<iostream>
using  namespace std;
void fun(string &str)
{
    str.pop_back();
}
int main()
{
    string s= "123456";
    cout << s << endl;
    fun(s);
    cout << s << endl;
    //删除某一段的数值
    s.erase(s.end()-2,s.end()-1);
    cout << s << endl;
}

8. find_if()

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/*
	find_if(begin,end,greatThree)
	找到大于三的所以所有数，return 首地址   就是一个数组
*/

#include<iostream> 
#include<algorithm> 
using namespace std;
bool greatThree(int x)
{
	if(x > 3) 
	return true;
	else
	return false;
}
template <class T>
void print(T x)
{
	cout << x << endl;
} 

int main()
{
	int a[10] = {1,2,3,4,5,6,7,8,9,10};
	int *p = find_if(a,a+10,greatThree) ;
	for(int i = 0;i < 7;i++)
	cout << *p++ <<endl;
	
	//for_each(a,a+9,print<int>) ;
}

9 find

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/*
	find返回找到元素的地址 
*/

#include<iostream> 
#include<algorithm> 
using namespace std;
template <class T>
void print(T x)
{
	cout << x << endl;
} 

int main()
{
	int a[10] = {1,2,3,4,5,6,7,8,9,10};
	cout << find(a,a+10,6);	
}

10.for_each()

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#include<iostream> 
#include<algorithm> 
using namespace std;
template <class T>
void print(T x)
{
	cout << x << endl;
} 

int main()
{
	int a[10] = {1,2,3,4,5,6,7,8,9,10};
	for_each(a,a+10,print<int>);
}

11.itoa

int类型换成char类型 还可以设置转换进制
十进制可以转换成任意进制

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/*
	int 类型换成string类型 
*/
#include<iostream> 
#include<stdlib.h> 
using namespace std;
int main()
{
	int a = 64;
	char b[3];
	itoa(a,b,8);  //8表示转换后的进制 
	cout << b[0] << b[1] << b[2];
}

12. max_element 和 min_element 求最大最小元素

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/*
	*max_element(begin,end)
	求最大成员 
*/
#include<iostream> 
#include<algorithm> 
using namespace std;
int main()
{
	int a[] = {1,2,5,6,3,4,8,9,7} ;
	cout << *max_element(a,a+9);
}

13. memset 初始化

  • 可以如下替代

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    #include<iostream>
    using namespace std;
    int main()
    {
        int a[10],b[10] = {1,2,3};
        for(int i = 0;i < 10;i++)
        cout << a[i] << " " << b[i] << endl;
    }

  • memset

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/*
	初始化数组 
*/
#include<iostream> 
#include<cstring> 
using namespace std;
int main()
{
	int a[10] ;
	memset(a,0,10);  //十个全部放0
	
}

14.replace_if() 满足条件的替换

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/*
	replace_if(begin,end,fun,int)将满足fun条件的换成int 
	replace(begin,end,3,5)		将所以的3替换成5 
*/

#include<iostream> 
#include<algorithm> 
using namespace std;
bool greatTree(int x) 
{
	if(x > 3)
		return true;
	else
		return false;
}
template <class T>
void print(T x)
{
	cout << x << endl;
} 

int main()
{
	int a[] = {1,2,3,4,5,6,7,8,9} ;
	replace_if(a,a+9,greatTree,9);//大于三的数替换成9 
	for_each(a,a+9,print<int>) ;
}

15.strstr() char*类型找到子串

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#include<iostream>
#include<cstring>
#include<string>
using namespace std;
int main()
{

    char* str = "I am a Android developer!";
    char* subStr = "Android";
    char* result = strstr(str, subStr);  //找到子串后面的字符串
    printf("result = %s\n", result);//结果：result = Android developer!
    return 0;
}

16. substr() 截取字符

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#include<iostream>
using namespace std;
int main()
{
   string str = "123456789";
    
    //__LONG_LONG_MAX__ a = 18374001125;
    cout << str.substr(2,3); //截取第i个字符后面三个
}

17.计时 getTIckCount()

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#include<stdio.h>
#include<iostream>
#include<windows.h>
using namespace  std;
int main()
{
    long n = 1000000000;
    long t1 = GetTickCount();
    //...娴嬭瘯浠ｇ爜
    while(n--);
    long t2 = GetTickCount();
    cout << "time:"<<(int(t2)-int(t1)) << endl;
    return 0;
}

18.toupper() 和 tolower 字符的变换

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#include<iostream>
using namespace std;
int main()
{
    string a = "oIu";
    a[0] = toupper(a[0]);
    a[0] = tolower(a[1]);
    cout << a;
}

19. 去重复unique() 必须已经排序

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#include<iostream>
#include<algorithm>
using namespace std;
void print(int a)
{
    cout <<a << " ";
}
int main()
{
    int a[6] ={1,1,2,2,3,3};
    for_each(a,a+6,print);
    cout << endl;
    int pos = unique(a,a+6)-a;
    for_each(a,a+6,print);
    cout << endl;
}

20. 判断isalpha()

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/*
	判断字符或数字 
*/

#include<iostream> 
#include<algorithm> 
using namespace std;

int main()
{
	char a = 'r' ,b = '1';
	if(isalpha(a))
	cout << "ok" ;
	if(isdigit(b))
	cout << "ko";
	
}

21. 取第k位数字

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#include<stdio.h> 
int len(int x){
    if(x<10) return 1;
    return len(x/10)+1;
}

// 取x的第k位数字
int f(int x, int k){
    if(len(x)-k==0) return x%10;
    return f(x/10,3);  //填空
}

int main()
{
    int x = 23574;
    printf("%d\n", f(x,3));
    return 0;
}

交并集

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#include<sstream>
#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
void print(int n)
{
    cout << n << " ";
}
int main()
{
  	vector<int> v1 = {1,2,3},v2={2,3,4},v3;
    //差集
    // set_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), inserter(v3, v3.begin()));
    // 交集
    // set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(), inserter(v3, v3.begin()));
    //并集
    set_union(v1.begin(), v1.end(), v2.begin(), v2.end(), inserter(v3, v3.begin()));
    v1 = v3;
    for_each(v1.begin(),v1.end(),print);
}

vector 通过值删除

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#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
void print(int n)
{
    cout << n << " ";
}
int main()
{
    vector<int> v={1,2,3,4,5};
    v.erase(remove(v.begin(),v.end(),3));
    for_each(v.begin(),v.end(),print);
}
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