cpp algorithm

今天在https://codility.com/ 上面测试了几道题，我发现用C++比用C 方便多了。因为如果用C++，我们可以使用STL 的结构及算法，但是使用C的话就要自己实现了。

毕业之后 就没有专门做过算法题了，今天使用起来有些生硬，费事不少。现在将一些常用结构整理一下，作为自己的知识库储存在大脑里，以后可以信手拈来。

一下提供一些C转C++的结构，以及C++常用算法。

1. 常用函数

get max integer

// numeric_limits example
#include <iostream>     // std::cout
#include <limits>       // std::numeric_limits

int main () {
std::cout << std::boolalpha;
std::cout << "Minimum value for int: " << std::numeric_limits<int>::min() << '\n';
std::cout << "Maximum value for int: " << std::numeric_limits<int>::max() << '\n';
std::cout << "int is signed: " << std::numeric_limits<int>::is_signed << '\n';
std::cout << "Non-sign bits in int: " << std::numeric_limits<int>::digits << '\n';
std::cout << "int has infinity: " << std::numeric_limits<int>::has_infinity << '\n';
return 0;
}

min, max

// min example
#include <iostream>     // std::cout
#include <algorithm>    // std::min

int main () {
std::cout << "min(1,2)==" << std::min(1,2) << '\n';
std::cout << "min(2,1)==" << std::min(2,1) << '\n';
std::cout << "min('a','z')==" << std::min('a','z') << '\n';
std::cout << "min(3.14,2.72)==" << std::min(3.14,2.72) << '\n';
return 0;
}

sort

// sort algorithm example
#include <iostream>     // std::cout
#include <algorithm>    // std::sort
#include <vector>       // std::vector

bool myfunction (int i,int j) { return (i<j); }

struct myclass {
bool operator() (int i,int j) { return (i<j);}
} myobject;

int main () {
int myints[] = {32,71,12,45,26,80,53,33};
std::vector<int> myvector (myints, myints+8);               // 32 71 12 45 26 80 53 33

// using default comparison (operator <):
std::sort (myvector.begin(), myvector.begin()+4);           //(12 32 45 71)26 80 53 33

// using function as comp
std::sort (myvector.begin()+4, myvector.end(), myfunction); // 12 32 45 71(26 33 53 80)

// using object as comp
std::sort (myvector.begin(), myvector.end(), myobject);     //(12 26 32 33 45 53 71 80)

// print out content:
std::cout << "myvector contains:";
for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
std::cout << ' ' << *it;
std::cout << '\n';

return 0;
}

std::count

// count algorithm example
#include <iostream>     // std::cout
#include <algorithm>    // std::count
#include <vector>       // std::vector

int main () {
// counting elements in array:
int myints[] = {10,20,30,30,20,10,10,20};   // 8 elements
int mycount = std::count (myints, myints+8, 10);
std::cout << "10 appears " << mycount << " times.\n";

// counting elements in container:
std::vector<int> myvector (myints, myints+8);
mycount = std::count (myvector.begin(), myvector.end(), 20);
std::cout << "20 appears " << mycount  << " times.\n";

return 0;
}

std::for_each

// for_each example
#include <iostream>     // std::cout
#include <algorithm>    // std::for_each
#include <vector>       // std::vector

void myfunction (int i) {  // function:
std::cout << ' ' << i;
}

struct myclass {           // function object type:
void operator() (int i) {std::cout << ' ' << i;}
} myobject;

int main () {
std::vector<int> myvector;
myvector.push_back(10);
myvector.push_back(20);
myvector.push_back(30);

std::cout << "myvector contains:";
for_each (myvector.begin(), myvector.end(), myfunction);
std::cout << '\n';

// or:
std::cout << "myvector contains:";
for_each (myvector.begin(), myvector.end(), myobject);
std::cout << '\n';

return 0;
}

2. C 的array转 C++ vector

vector 的构造函数如下所示，

// constructors used in the same order as described above:
std::vector<int> first;                                // empty vector of ints
std::vector<int> second (4,100);                       // four ints with value 100
std::vector<int> third (second.begin(),second.end());  // iterating through second
std::vector<int> fourth (third);                       // a copy of third

// the iterator constructor can also be used to construct from arrays:
int myints[] = {16,2,77,29};
std::vector<int> fifth (myints, myints + sizeof(myints) / sizeof(int) )

int A[] = {1, 2, 3, 4, 5}

std::vector<int> vec(A, A+sizeouf(A)/sizeof(int)) //

3. 常用算法

1）动态规划例子

最长公共子序列：给定两个数组A和B，求其最长公共子序列。

最长递增子序列：给定数组A, 求其最长递增子序列。